Add a bulk interface to sem_down()

[akaros.git] / kern / src / schedule.c

/* Copyright (c) 2009, 2012 The Regents of the University of California
 * Barret Rhoden <brho@cs.berkeley.edu>
 * See LICENSE for details.
 *
 * Scheduling and dispatching. */

#include <schedule.h>
#include <corerequest.h>
#include <process.h>
#include <monitor.h>
#include <stdio.h>
#include <assert.h>
#include <atomic.h>
#include <smp.h>
#include <manager.h>
#include <alarm.h>
#include <sys/queue.h>
#include <arsc_server.h>
#include <hashtable.h>

/* Process Lists.  'unrunnable' is a holding list for SCPs that are running or
 * waiting or otherwise not considered for sched decisions. */
struct proc_list unrunnable_scps = TAILQ_HEAD_INITIALIZER(unrunnable_scps);
struct proc_list runnable_scps = TAILQ_HEAD_INITIALIZER(runnable_scps);
/* mcp lists.  we actually could get by with one list and a TAILQ_CONCAT, but
 * I'm expecting to want the flexibility of the pointers later. */
struct proc_list all_mcps_1 = TAILQ_HEAD_INITIALIZER(all_mcps_1);
struct proc_list all_mcps_2 = TAILQ_HEAD_INITIALIZER(all_mcps_2);
struct proc_list *primary_mcps = &all_mcps_1;
struct proc_list *secondary_mcps = &all_mcps_2;

/* Helper, defined below */
static void __core_request(struct proc *p, uint32_t amt_needed);
static void add_to_list(struct proc *p, struct proc_list *list);
static void remove_from_list(struct proc *p, struct proc_list *list);
static void switch_lists(struct proc *p, struct proc_list *old,
                         struct proc_list *new);
static void __run_mcp_ksched(void *arg);        /* don't call directly */
static uint32_t get_cores_needed(struct proc *p);

/* Locks / sync tools */

/* poke-style ksched - ensures the MCP ksched only runs once at a time.  since
 * only one mcp ksched runs at a time, while this is set, the ksched knows no
 * cores are being allocated by other code (though they could be dealloc, due to
 * yield).
 *
 * The main value to this sync method is to make the 'make sure the ksched runs
 * only once at a time and that it actually runs' invariant/desire wait-free, so
 * that it can be called anywhere (deep event code, etc).
 *
 * As the ksched gets smarter, we'll probably embedd this poker in a bigger
 * struct that can handle the posting of different types of work. */
struct poke_tracker ksched_poker = POKE_INITIALIZER(__run_mcp_ksched);

/* this 'big ksched lock' protects a bunch of things, which i may make fine
 * grained: */
/* - protects the integrity of proc tailqs/structures, as well as the membership
 * of a proc on those lists.  proc lifetime within the ksched but outside this
 * lock is protected by the proc kref. */
//spinlock_t proclist_lock = SPINLOCK_INITIALIZER; /* subsumed by bksl */
/* - protects the provisioning assignment, and the integrity of all prov
 * lists (the lists of each proc). */
//spinlock_t prov_lock = SPINLOCK_INITIALIZER;
/* - protects allocation structures */
//spinlock_t alloc_lock = SPINLOCK_INITIALIZER;
spinlock_t sched_lock = SPINLOCK_INITIALIZER;

/* Alarm struct, for our example 'timer tick' */
struct alarm_waiter ksched_waiter;

#define TIMER_TICK_USEC 10000   /* 10msec */

/* Helper: Sets up a timer tick on the calling core to go off 10 msec from now.
 * This assumes the calling core is an LL core, etc. */
static void set_ksched_alarm(void)
{
        set_awaiter_rel(&ksched_waiter, TIMER_TICK_USEC);
        set_alarm(&per_cpu_info[core_id()].tchain, &ksched_waiter);
}

/* Need a kmsg to just run the sched, but not to rearm */
static void __just_sched(uint32_t srcid, long a0, long a1, long a2)
{
        run_scheduler();
}

/* RKM alarm, to run the scheduler tick (not in interrupt context) and reset the
 * alarm.  Note that interrupts will be disabled, but this is not the same as
 * interrupt context.  We're a routine kmsg, which means the core is in a
 * quiescent state. */
static void __ksched_tick(struct alarm_waiter *waiter)
{
        /* TODO: imagine doing some accounting here */
        run_scheduler();
        /* Set our alarm to go off, relative to now.  This means we might lag a bit,
         * and our ticks won't match wall clock time.  But if we do incremental,
         * we'll actually punish the next process because the kernel took too long
         * for the previous process.  Ultimately, if we really care, we should
         * account for the actual time used. */
        set_awaiter_rel(&ksched_waiter, TIMER_TICK_USEC);
        set_alarm(&per_cpu_info[core_id()].tchain, &ksched_waiter);
}

void schedule_init(void)
{
        spin_lock(&sched_lock);
        assert(!core_id());             /* want the alarm on core0 for now */
        init_awaiter(&ksched_waiter, __ksched_tick);
        set_ksched_alarm();
        corealloc_init();
        spin_unlock(&sched_lock);

#ifdef CONFIG_ARSC_SERVER
        /* Most likely we'll have a syscall and a process that dedicates itself to
         * running this.  Or if it's a kthread, we don't need a core. */
        #error "Find a way to get a core.  Probably a syscall to run a server."
        int arsc_coreid = get_any_idle_core();
        assert(arsc_coreid >= 0);
        send_kernel_message(arsc_coreid, arsc_server, 0, 0, 0, KMSG_ROUTINE);
        printk("Using core %d for the ARSC server\n", arsc_coreid);
#endif /* CONFIG_ARSC_SERVER */
}

/* Round-robins on whatever list it's on */
static void add_to_list(struct proc *p, struct proc_list *new)
{
        assert(!(p->ksched_data.cur_list));
        TAILQ_INSERT_TAIL(new, p, ksched_data.proc_link);
        p->ksched_data.cur_list = new;
}

static void remove_from_list(struct proc *p, struct proc_list *old)
{
        assert(p->ksched_data.cur_list == old);
        TAILQ_REMOVE(old, p, ksched_data.proc_link);
        p->ksched_data.cur_list = 0;
}

static void switch_lists(struct proc *p, struct proc_list *old,
                         struct proc_list *new)
{
        remove_from_list(p, old);
        add_to_list(p, new);
}

/* Removes from whatever list p is on */
static void remove_from_any_list(struct proc *p)
{
        if (p->ksched_data.cur_list) {
                TAILQ_REMOVE(p->ksched_data.cur_list, p, ksched_data.proc_link);
                p->ksched_data.cur_list = 0;
        }
}

/************** Process Management Callbacks **************/
/* a couple notes:
 * - the proc lock is NOT held for any of these calls.  currently, there is no
 *   lock ordering between the sched lock and the proc lock.  since the proc
 *   code doesn't know what we do, it doesn't hold its lock when calling our
 *   CBs.
 * - since the proc lock isn't held, the proc could be dying, which means we
 *   will receive a __sched_proc_destroy() either before or after some of these
 *   other CBs.  the CBs related to list management need to check and abort if
 *   DYING */
void __sched_proc_register(struct proc *p)
{
        assert(!proc_is_dying(p));              /* shouldn't be able to happen yet */
        /* one ref for the proc's existence, cradle-to-grave */
        proc_incref(p, 1);      /* need at least this OR the 'one for existing' */
        spin_lock(&sched_lock);
        corealloc_proc_init(p);
        add_to_list(p, &unrunnable_scps);
        spin_unlock(&sched_lock);
}

/* Returns 0 if it succeeded, an error code otherwise. */
void __sched_proc_change_to_m(struct proc *p)
{
        spin_lock(&sched_lock);
        /* Need to make sure they aren't dying.  if so, we already dealt with their
         * list membership, etc (or soon will).  taking advantage of the 'immutable
         * state' of dying (so long as refs are held). */
        if (proc_is_dying(p)) {
                spin_unlock(&sched_lock);
                return;
        }
        /* Catch user bugs */
        if (!p->procdata->res_req[RES_CORES].amt_wanted) {
                printk("[kernel] process needs to specify amt_wanted\n");
                p->procdata->res_req[RES_CORES].amt_wanted = 1;
        }
        /* For now, this should only ever be called on an unrunnable.  It's
         * probably a bug, at this stage in development, to do o/w. */
        remove_from_list(p, &unrunnable_scps);
        //remove_from_any_list(p);      /* ^^ instead of this */
        add_to_list(p, primary_mcps);
        spin_unlock(&sched_lock);
        //poke_ksched(p, RES_CORES);
}

/* Sched callback called when the proc dies.  pc_arr holds the cores the proc
 * had, if any, and nr_cores tells us how many are in the array.
 *
 * An external, edible ref is passed in.  when we return and they decref,
 * __proc_free will be called (when the last one is done). */
void __sched_proc_destroy(struct proc *p, uint32_t *pc_arr, uint32_t nr_cores)
{
        spin_lock(&sched_lock);
        /* Unprovision any cores.  Note this is different than track_core_dealloc.
         * The latter does bookkeeping when an allocation changes.  This is a
         * bulk *provisioning* change. */
        __unprovision_all_cores(p);
        /* Remove from whatever list we are on (if any - might not be on one if it
         * was in the middle of __run_mcp_sched) */
        remove_from_any_list(p);
        if (nr_cores)
                __track_core_dealloc_bulk(p, pc_arr, nr_cores);
        spin_unlock(&sched_lock);
        /* Drop the cradle-to-the-grave reference, jet-li */
        proc_decref(p);
}

/* ksched callbacks.  p just woke up and is UNLOCKED. */
void __sched_mcp_wakeup(struct proc *p)
{
        spin_lock(&sched_lock);
        if (proc_is_dying(p)) {
                spin_unlock(&sched_lock);
                return;
        }
        /* could try and prioritize p somehow (move it to the front of the list). */
        spin_unlock(&sched_lock);
        /* note they could be dying at this point too. */
        poke(&ksched_poker, p);
}

/* ksched callbacks.  p just woke up and is UNLOCKED. */
void __sched_scp_wakeup(struct proc *p)
{
        spin_lock(&sched_lock);
        if (proc_is_dying(p)) {
                spin_unlock(&sched_lock);
                return;
        }
        /* might not be on a list if it is new.  o/w, it should be unrunnable */
        remove_from_any_list(p);
        add_to_list(p, &runnable_scps);
        spin_unlock(&sched_lock);
        /* we could be on a CG core, and all the mgmt cores could be halted.  if we
         * don't tell one of them about the new proc, they will sleep until the
         * timer tick goes off. */
        if (!management_core()) {
                /* TODO: pick a better core and only send if halted.
                 *
                 * ideally, we'd know if a specific mgmt core is sleeping and wake it
                 * up.  o/w, we could interrupt an already-running mgmt core that won't
                 * get to our new proc anytime soon.  also, by poking core 0, a
                 * different mgmt core could remain idle (and this process would sleep)
                 * until its tick goes off */
                send_ipi(0, I_POKE_CORE);
        }
}

/* Callback to return a core to the ksched, which tracks it as idle and
 * deallocated from p.  The proclock is held (__core_req depends on that).
 *
 * This also is a trigger, telling us we have more cores.  We could/should make
 * a scheduling decision (or at least plan to). */
void __sched_put_idle_core(struct proc *p, uint32_t coreid)
{
        spin_lock(&sched_lock);
        __track_core_dealloc(p, coreid);
        spin_unlock(&sched_lock);
}

/* Callback, bulk interface for put_idle. The proclock is held for this. */
void __sched_put_idle_cores(struct proc *p, uint32_t *pc_arr, uint32_t num)
{
        spin_lock(&sched_lock);
        __track_core_dealloc_bulk(p, pc_arr, num);
        spin_unlock(&sched_lock);
        /* could trigger a sched decision here */
}

/* mgmt/LL cores should call this to schedule the calling core and give it to an
 * SCP.  will also prune the dead SCPs from the list.  hold the lock before
 * calling.  returns TRUE if it scheduled a proc. */
static bool __schedule_scp(void)
{
        // TODO: sort out lock ordering (proc_run_s also locks)
        struct proc *p;
        uint32_t pcoreid = core_id();
        struct per_cpu_info *pcpui = &per_cpu_info[pcoreid];
        /* if there are any runnables, run them here and put any currently running
         * SCP on the tail of the runnable queue. */
        if ((p = TAILQ_FIRST(&runnable_scps))) {
                /* someone is currently running, dequeue them */
                if (pcpui->owning_proc) {
                        spin_lock(&pcpui->owning_proc->proc_lock);
                        /* process might be dying, with a KMSG to clean it up waiting on
                         * this core.  can't do much, so we'll attempt to restart */
                        if (proc_is_dying(pcpui->owning_proc)) {
                                send_kernel_message(core_id(), __just_sched, 0, 0, 0,
                                                    KMSG_ROUTINE);
                                spin_unlock(&pcpui->owning_proc->proc_lock);
                                return FALSE;
                        }
                        printd("Descheduled %d in favor of %d\n", pcpui->owning_proc->pid,
                               p->pid);
                        __proc_set_state(pcpui->owning_proc, PROC_RUNNABLE_S);
                        /* Saving FP state aggressively.  Odds are, the SCP was hit by an
                         * IRQ and has a HW ctx, in which case we must save. */
                        __proc_save_fpu_s(pcpui->owning_proc);
                        __proc_save_context_s(pcpui->owning_proc);
                        vcore_account_offline(pcpui->owning_proc, 0);
                        __seq_start_write(&p->procinfo->coremap_seqctr);
                        __unmap_vcore(p, 0);
                        __seq_end_write(&p->procinfo->coremap_seqctr);
                        spin_unlock(&pcpui->owning_proc->proc_lock);
                        /* round-robin the SCPs (inserts at the end of the queue) */
                        switch_lists(pcpui->owning_proc, &unrunnable_scps, &runnable_scps);
                        clear_owning_proc(pcoreid);
                        /* Note we abandon core.  It's not strictly necessary.  If
                         * we didn't, the TLB would still be loaded with the old
                         * one, til we proc_run_s, and the various paths in
                         * proc_run_s would pick it up.  This way is a bit safer for
                         * future changes, but has an extra (empty) TLB flush.  */
                        abandon_core();
                }
                /* Run the new proc */
                switch_lists(p, &runnable_scps, &unrunnable_scps);
                printd("PID of the SCP i'm running: %d\n", p->pid);
                proc_run_s(p);  /* gives it core we're running on */
                return TRUE;
        }
        return FALSE;
}

/* Returns how many new cores p needs.  This doesn't lock the proc, so your
 * answer might be stale. */
static uint32_t get_cores_needed(struct proc *p)
{
        uint32_t amt_wanted, amt_granted;
        amt_wanted = p->procdata->res_req[RES_CORES].amt_wanted;
        /* Help them out - if they ask for something impossible, give them 1 so they
         * can make some progress. (this is racy, and unnecessary). */
        if (amt_wanted > p->procinfo->max_vcores) {
                printk("[kernel] proc %d wanted more than max, wanted %d\n", p->pid,
                       amt_wanted);
                p->procdata->res_req[RES_CORES].amt_wanted = 1;
                amt_wanted = 1;
        }
        /* There are a few cases where amt_wanted is 0, but they are still RUNNABLE
         * (involving yields, events, and preemptions).  In these cases, give them
         * at least 1, so they can make progress and yield properly.  If they are
         * not WAITING, they did not yield and may have missed a message. */
        if (!amt_wanted) {
                /* could ++, but there could be a race and we don't want to give them
                 * more than they ever asked for (in case they haven't prepped) */
                p->procdata->res_req[RES_CORES].amt_wanted = 1;
                amt_wanted = 1;
        }
        /* amt_granted is racy - they could be *yielding*, but currently they can't
         * be getting any new cores if the caller is in the mcp_ksched.  this is
         * okay - we won't accidentally give them more cores than they *ever* wanted
         * (which could crash them), but our answer might be a little stale. */
        amt_granted = p->procinfo->res_grant[RES_CORES];
        /* Do not do an assert like this: it could fail (yield in progress): */
        //assert(amt_granted == p->procinfo->num_vcores);
        if (amt_wanted <= amt_granted)
                return 0;
        return amt_wanted - amt_granted;
}

/* Actual work of the MCP kscheduler.  if we were called by poke_ksched, *arg
 * might be the process who wanted special service.  this would be the case if
 * we weren't already running the ksched.  Sort of a ghetto way to "post work",
 * such that it's an optimization. */
static void __run_mcp_ksched(void *arg)
{
        struct proc *p, *temp;
        uint32_t amt_needed;
        struct proc_list *temp_mcp_list;
        /* locking to protect the MCP lists' integrity and membership */
        spin_lock(&sched_lock);
        /* 2-pass scheme: check each proc on the primary list (FCFS).  if they need
         * nothing, put them on the secondary list.  if they need something, rip
         * them off the list, service them, and if they are still not dying, put
         * them on the secondary list.  We cull the entire primary list, so that
         * when we start from the beginning each time, we aren't repeatedly checking
         * procs we looked at on previous waves.
         *
         * TODO: we could modify this such that procs that we failed to service move
         * to yet another list or something.  We can also move the WAITINGs to
         * another list and have wakeup move them back, etc. */
        while (!TAILQ_EMPTY(primary_mcps)) {
                TAILQ_FOREACH_SAFE(p, primary_mcps, ksched_data.proc_link, temp) {
                        if (p->state == PROC_WAITING) { /* unlocked peek at the state */
                                switch_lists(p, primary_mcps, secondary_mcps);
                                continue;
                        }
                        amt_needed = get_cores_needed(p);
                        if (!amt_needed) {
                                switch_lists(p, primary_mcps, secondary_mcps);
                                continue;
                        }
                        /* o/w, we want to give cores to this proc */
                        remove_from_list(p, primary_mcps);
                        /* now it won't die, but it could get removed from lists and have
                         * its stuff unprov'd when we unlock */
                        proc_incref(p, 1);
                        /* GIANT WARNING: __core_req will unlock the sched lock for a bit.
                         * It will return with it locked still.  We could unlock before we
                         * pass in, but they will relock right away. */
                        // notionally_unlock(&ksched_lock);     /* for mouse-eyed viewers */
                        __core_request(p, amt_needed);
                        // notionally_lock(&ksched_lock);
                        /* Peeking at the state is okay, since we hold a ref.  Once it is
                         * DYING, it'll remain DYING until we decref.  And if there is a
                         * concurrent death, that will spin on the ksched lock (which we
                         * hold, and which protects the proc lists). */
                        if (!proc_is_dying(p))
                                add_to_list(p, secondary_mcps);
                        proc_decref(p);                 /* fyi, this may trigger __proc_free */
                        /* need to break: the proc lists may have changed when we unlocked
                         * in core_req in ways that the FOREACH_SAFE can't handle. */
                        break;
                }
        }
        /* at this point, we moved all the procs over to the secondary list, and
         * attempted to service the ones that wanted something.  now just swap the
         * lists for the next invocation of the ksched. */
        temp_mcp_list = primary_mcps;
        primary_mcps = secondary_mcps;
        secondary_mcps = temp_mcp_list;
        spin_unlock(&sched_lock);
}

/* Something has changed, and for whatever reason the scheduler should
 * reevaluate things.
 *
 * Don't call this if you are processing a syscall or otherwise care about your
 * kthread variables, cur_proc/owning_proc, etc.
 *
 * Don't call this from interrupt context (grabs proclocks). */
void run_scheduler(void)
{
        /* MCP scheduling: post work, then poke.  for now, i just want the func to
         * run again, so merely a poke is sufficient. */
        poke(&ksched_poker, 0);
        if (management_core()) {
                spin_lock(&sched_lock);
                __schedule_scp();
                spin_unlock(&sched_lock);
        }
}

/* A process is asking the ksched to look at its resource desires.  The
 * scheduler is free to ignore this, for its own reasons, so long as it
 * eventually gets around to looking at resource desires. */
void poke_ksched(struct proc *p, unsigned int res_type)
{
        /* ignoring res_type for now.  could post that if we wanted (would need some
         * other structs/flags) */
        if (!__proc_is_mcp(p))
                return;
        poke(&ksched_poker, p);
}

/* The calling cpu/core has nothing to do and plans to idle/halt.  This is an
 * opportunity to pick the nature of that halting (low power state, etc), or
 * provide some other work (_Ss on LL cores).  Note that interrupts are
 * disabled, and if you return, the core will cpu_halt(). */
void cpu_bored(void)
{
        bool new_proc = FALSE;
        if (!management_core())
                return;
        spin_lock(&sched_lock);
        new_proc = __schedule_scp();
        spin_unlock(&sched_lock);
        /* if we just scheduled a proc, we need to manually restart it, instead of
         * returning.  if we return, the core will halt. */
        if (new_proc) {
                proc_restartcore();
                assert(0);
        }
        /* Could drop into the monitor if there are no processes at all.  For now,
         * the 'call of the giraffe' suffices. */
}

/* Available resources changed (plus or minus).  Some parts of the kernel may
 * call this if a particular resource that is 'quantity-based' changes.  Things
 * like available RAM to processes, bandwidth, etc.  Cores would probably be
 * inappropriate, since we need to know which specific core is now free. */
void avail_res_changed(int res_type, long change)
{
        printk("[kernel] ksched doesn't track any resources yet!\n");
}

/* This deals with a request for more cores.  The amt of new cores needed is
 * passed in.  The ksched lock is held, but we are free to unlock if we want
 * (and we must, if calling out of the ksched to anything high-level).
 *
 * Side note: if we want to warn, then we can't deal with this proc's prov'd
 * cores until we wait til the alarm goes off.  would need to put all
 * alarmed cores on a list and wait til the alarm goes off to do the full
 * preempt.  and when those cores come in voluntarily, we'd need to know to
 * give them to this proc. */
static void __core_request(struct proc *p, uint32_t amt_needed)
{
        uint32_t nr_to_grant = 0;
        uint32_t corelist[num_cores];
        uint32_t pcoreid;
        struct proc *proc_to_preempt;
        bool success;
        /* we come in holding the ksched lock, and we hold it here to protect
         * allocations and provisioning. */
        /* get all available cores from their prov_not_alloc list.  the list might
         * change when we unlock (new cores added to it, or the entire list emptied,
         * but no core allocations will happen (we hold the poke)). */
        while (nr_to_grant != amt_needed) {
                /* Find the next best core to allocate to p. It may be a core
                 * provisioned to p, and it might not be. */
                pcoreid = __find_best_core_to_alloc(p);
                /* If no core is returned, we know that there are no more cores to give
                 * out, so we exit the loop. */
                if (pcoreid == -1)
                        break;
                /* If the pcore chosen currently has a proc allocated to it, we know
                 * it must be provisioned to p, but not allocated to it. We need to try
                 * to preempt. After this block, the core will be track_dealloc'd and
                 * on the idle list (regardless of whether we had to preempt or not) */
                if (get_alloc_proc(pcoreid)) {
                        proc_to_preempt = get_alloc_proc(pcoreid);
                        /* would break both preemption and maybe the later decref */
                        assert(proc_to_preempt != p);
                        /* need to keep a valid, external ref when we unlock */
                        proc_incref(proc_to_preempt, 1);
                        spin_unlock(&sched_lock);
                        /* sending no warning time for now - just an immediate preempt. */
                        success = proc_preempt_core(proc_to_preempt, pcoreid, 0);
                        /* reaquire locks to protect provisioning and idle lists */
                        spin_lock(&sched_lock);
                        if (success) {
                                /* we preempted it before the proc could yield or die.
                                 * alloc_proc should not have changed (it'll change in death and
                                 * idle CBs).  the core is not on the idle core list.  (if we
                                 * ever have proc alloc lists, it'll still be on the old proc's
                                 * list). */
                                assert(get_alloc_proc(pcoreid));
                                /* regardless of whether or not it is still prov to p, we need
                                 * to note its dealloc.  we are doing some excessive checking of
                                 * p == prov_proc, but using this helper is a lot clearer. */
                                __track_core_dealloc(proc_to_preempt, pcoreid);
                        } else {
                                /* the preempt failed, which should only happen if the pcore was
                                 * unmapped (could be dying, could be yielding, but NOT
                                 * preempted).  whoever unmapped it also triggered (or will soon
                                 * trigger) a track_core_dealloc and put it on the idle list.
                                 * Our signal for this is get_alloc_proc() being 0. We need to
                                 * spin and let whoever is trying to free the core grab the
                                 * ksched lock.  We could use an 'ignore_next_idle' flag per
                                 * sched_pcore, but it's not critical anymore.
                                 *
                                 * Note, we're relying on us being the only preemptor - if the
                                 * core was unmapped by *another* preemptor, there would be no
                                 * way of knowing the core was made idle *yet* (the success
                                 * branch in another thread).  likewise, if there were another
                                 * allocator, the pcore could have been put on the idle list and
                                 * then quickly removed/allocated. */
                                cmb();
                                while (get_alloc_proc(pcoreid)) {
                                        /* this loop should be very rare */
                                        spin_unlock(&sched_lock);
                                        udelay(1);
                                        spin_lock(&sched_lock);
                                }
                        }
                        /* no longer need to keep p_to_pre alive */
                        proc_decref(proc_to_preempt);
                        /* might not be prov to p anymore (rare race). pcoreid is idle - we
                         * might get it later, or maybe we'll give it to its rightful proc*/
                        if (get_prov_proc(pcoreid) != p)
                                continue;
                }
                /* At this point, the pcore is idle, regardless of how we got here
                 * (successful preempt, failed preempt, or it was idle in the first
                 * place).  We also know the core is still provisioned to us.  Lets add
                 * it to the corelist for p (so we can give it to p in bulk later), and
                 * track its allocation with p (so our internal data structures stay in
                 * sync). We rely on the fact that we are the only allocator (pcoreid is
                 * still idle, despite (potentially) unlocking during the preempt
                 * attempt above).  It is guaranteed to be track_dealloc'd()
                 * (regardless of how we got here). */
                corelist[nr_to_grant] = pcoreid;
                nr_to_grant++;
                __track_core_alloc(p, pcoreid);
        }
        /* Now, actually give them out */
        if (nr_to_grant) {
                /* Need to unlock before calling out to proc code.  We are somewhat
                 * relying on being the only one allocating 'thread' here, since another
                 * allocator could have seen these cores (if they are prov to some proc)
                 * and could be trying to give them out (and assuming they are already
                 * on the idle list). */
                spin_unlock(&sched_lock);
                /* give them the cores.  this will start up the extras if RUNNING_M. */
                spin_lock(&p->proc_lock);
                /* if they fail, it is because they are WAITING or DYING.  we could give
                 * the cores to another proc or whatever.  for the current type of
                 * ksched, we'll just put them back on the pile and return.  Note, the
                 * ksched could check the states after locking, but it isn't necessary:
                 * just need to check at some point in the ksched loop. */
                if (__proc_give_cores(p, corelist, nr_to_grant)) {
                        spin_unlock(&p->proc_lock);
                        /* we failed, put the cores and track their dealloc.  lock is
                         * protecting those structures. */
                        spin_lock(&sched_lock);
                        __track_core_dealloc_bulk(p, corelist, nr_to_grant);
                } else {
                        /* at some point after giving cores, call proc_run_m() (harmless on
                         * RUNNING_Ms).  You can give small groups of cores, then run them
                         * (which is more efficient than interleaving runs with the gives
                         * for bulk preempted processes). */
                        __proc_run_m(p);
                        spin_unlock(&p->proc_lock);
                        /* main mcp_ksched wants this held (it came to __core_req held) */
                        spin_lock(&sched_lock);
                }
        }
        /* note the ksched lock is still held */
}

/* Provision a core to a process. This function wraps the primary logic
 * implemented in __provision_core, with a lock, error checking, etc. */
int provision_core(struct proc *p, uint32_t pcoreid)
{
        /* Make sure we aren't asking for something that doesn't exist (bounds check
         * on the pcore array) */
        if (!(pcoreid < num_cores)) {
                set_errno(ENXIO);
                return -1;
        }
        /* Don't allow the provisioning of LL cores */
        if (is_ll_core(pcoreid)) {
                set_errno(EBUSY);
                return -1;
        }
        /* Note the sched lock protects the tailqs for all procs in this code.
         * If we need a finer grained sched lock, this is one place where we could
         * have a different lock */
        spin_lock(&sched_lock);
        __provision_core(p, pcoreid);
        spin_unlock(&sched_lock);
        return 0;
}

/************** Debugging **************/
void sched_diag(void)
{
        struct proc *p;
        spin_lock(&sched_lock);
        TAILQ_FOREACH(p, &runnable_scps, ksched_data.proc_link)
                printk("Runnable _S PID: %d\n", p->pid);
        TAILQ_FOREACH(p, &unrunnable_scps, ksched_data.proc_link)
                printk("Unrunnable _S PID: %d\n", p->pid);
        TAILQ_FOREACH(p, primary_mcps, ksched_data.proc_link)
                printk("Primary MCP PID: %d\n", p->pid);
        TAILQ_FOREACH(p, secondary_mcps, ksched_data.proc_link)
                printk("Secondary MCP PID: %d\n", p->pid);
        spin_unlock(&sched_lock);
        return;
}

void print_resources(struct proc *p)
{
        printk("--------------------\n");
        printk("PID: %d\n", p->pid);
        printk("--------------------\n");
        for (int i = 0; i < MAX_NUM_RESOURCES; i++)
                printk("Res type: %02d, amt wanted: %08d, amt granted: %08d\n", i,
                       p->procdata->res_req[i].amt_wanted, p->procinfo->res_grant[i]);
}

void print_all_resources(void)
{
        /* Hash helper */
        void __print_resources(void *item, void *opaque)
        {
                print_resources((struct proc*)item);
        }
        spin_lock(&pid_hash_lock);
        hash_for_each(pid_hash, __print_resources, NULL);
        spin_unlock(&pid_hash_lock);
}

void next_core_to_alloc(uint32_t pcoreid)
{
        spin_lock(&sched_lock);
        __next_core_to_alloc(pcoreid);
        spin_unlock(&sched_lock);
}

void sort_idle_cores(void)
{
        spin_lock(&sched_lock);
        __sort_idle_cores();
        spin_unlock(&sched_lock);
}