Date: Tue, 21 Jul 2026 02:26:57 +0000 From: Olivier Certner <olce@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Cc: Minsoo Choo <minsoo@minsoo.io> Subject: git: deddfa3db956 - main - sched_4bsd: Allocate runqueues only for present CPUs Message-ID: <6a5ed8f1.21412.5ac576b6@gitrepo.freebsd.org>
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The branch main has been updated by olce: URL: https://cgit.FreeBSD.org/src/commit/?id=deddfa3db956ebed584a859010a10b6d9a4e2e5d commit deddfa3db956ebed584a859010a10b6d9a4e2e5d Author: Minsoo Choo <minsoo@minsoo.io> AuthorDate: 2026-07-20 02:37:56 +0000 Commit: Olivier Certner <olce@FreeBSD.org> CommitDate: 2026-07-21 02:24:18 +0000 sched_4bsd: Allocate runqueues only for present CPUs 4BSD has been allocating an array of MAXCPU runqueues, runq_pcpu[], instead of one runqueue per actually present CPU. On amd64, MAXCPU is 1024 and 'struct runq' is 4128 bytes, causing runq_pcpu[] to take more than 4 MiB of memory. On the vast majority of current systems, which have at most 32 cores with SMT, this is a waste of memory. Besides providing per-CPU runqueues, runq_pcpu[] has also been used to determine the CPU ID of a given thread's associated runqueue through pointer arithmetic. Since per-CPU structures are only allocated for present CPUs, in order to save space, move the runqueues to per-CPU fields and, for each thread ('struct ts_sched'), replace its runqueue pointer by the CPU ID of the runqueue it is in (new 'ts_rqcpu' field). Set the thread's CPU ID to the special NOCPU value when it is running on the global runqueue. Drop the SKE_RUNQ_PCPU() macro as it is now simply equivalent to 'ts_rqcpu != NOCPU'. Introduce the TS_RUNQ_PTR() macro to get a pointer to the thread's runqueue, which must be passed to runq_add() and runq_remove(). [olce: Massaged the commit message. Fixed an inverted KASSERT(). Tested with source builds.] Reviewed by: olce Tested by: olce MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D58000 --- sys/kern/sched_4bsd.c | 57 +++++++++++++++++++++++++++------------------------ 1 file changed, 30 insertions(+), 27 deletions(-) diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c index 11dc2fbcec5b..9c3a8821e2c9 100644 --- a/sys/kern/sched_4bsd.c +++ b/sys/kern/sched_4bsd.c @@ -93,7 +93,7 @@ struct td_sched { int ts_slptime; /* Seconds !RUNNING. */ int ts_slice; /* Remaining part of time slice. */ int ts_flags; - struct runq *ts_runq; /* runq the thread is currently on */ + int ts_rqcpu; /* That CPU's runq or NOCPU => global */ #ifdef KTR char ts_name[TS_NAME_LEN]; #endif @@ -109,8 +109,12 @@ struct td_sched { /* flags kept in ts_flags */ #define TSF_AFFINITY 0x0001 /* Has a non-"full" CPU set. */ -#define SKE_RUNQ_PCPU(ts) \ - ((ts)->ts_runq != 0 && (ts)->ts_runq != &runq_global) +#ifdef SMP +#define TS_RUNQ_PTR(ts) ((ts)->ts_rqcpu == NOCPU ? \ + (&runq_global) : (DPCPU_ID_PTR((ts)->ts_rqcpu, runq_pcpu))) +#else +#define TS_RUNQ_PTR(ts) (&runq_global) +#endif #define THREAD_CAN_SCHED(td, cpu) \ CPU_ISSET((cpu), &(td)->td_cpuset->cs_mask) @@ -160,8 +164,8 @@ static struct runq runq_global; /* * Per-CPU run queues */ -static struct runq runq_pcpu[MAXCPU]; -long runq_length[MAXCPU]; +DPCPU_DEFINE_STATIC(struct runq, runq_pcpu); +DPCPU_DEFINE_STATIC(long, runq_length); static cpuset_t idle_cpus_mask; #endif @@ -176,10 +180,10 @@ static void setup_runqs(void) { #ifdef SMP - int i; + int cpu; - for (i = 0; i < MAXCPU; ++i) - runq_init(&runq_pcpu[i]); + CPU_FOREACH(cpu) + runq_init(DPCPU_ID_PTR(cpu, runq_pcpu)); #endif runq_init(&runq_global); @@ -683,7 +687,7 @@ sched_4bsd_runnable(void) { #ifdef SMP return (runq_not_empty(&runq_global) || - runq_not_empty(&runq_pcpu[PCPU_GET(cpuid)])); + runq_not_empty(DPCPU_PTR(runq_pcpu))); #else return (runq_not_empty(&runq_global)); #endif @@ -1291,7 +1295,7 @@ sched_pickcpu(struct thread *td) if (best == NOCPU) best = cpu; - else if (runq_length[cpu] < runq_length[best]) + else if (DPCPU_ID_GET(cpu, runq_length) < DPCPU_ID_GET(best, runq_length)) best = cpu; } KASSERT(best != NOCPU, ("no valid CPUs")); @@ -1355,13 +1359,13 @@ sched_4bsd_add(struct thread *td, int flags) cpu = td->td_lastcpu; else if (td->td_flags & TDF_BOUND) { /* Find CPU from bound runq. */ - KASSERT(SKE_RUNQ_PCPU(ts), + KASSERT(ts->ts_rqcpu != NOCPU, ("sched_add: bound td_sched not on cpu runq")); - cpu = ts->ts_runq - &runq_pcpu[0]; + cpu = ts->ts_rqcpu; } else /* Find a valid CPU for our cpuset */ cpu = sched_pickcpu(td); - ts->ts_runq = &runq_pcpu[cpu]; + ts->ts_rqcpu = cpu; single_cpu = 1; CTR3(KTR_RUNQ, "sched_add: Put td_sched:%p(td:%p) on cpu%d runq", ts, td, @@ -1371,14 +1375,14 @@ sched_4bsd_add(struct thread *td, int flags) "sched_add: adding td_sched:%p (td:%p) to gbl runq", ts, td); cpu = NOCPU; - ts->ts_runq = &runq_global; + ts->ts_rqcpu = NOCPU; } if ((td->td_flags & TDF_NOLOAD) == 0) sched_load_add(); - runq_add(ts->ts_runq, td, flags); + runq_add(TS_RUNQ_PTR(ts), td, flags); if (cpu != NOCPU) - runq_length[cpu]++; + (*DPCPU_ID_PTR(cpu, runq_length))++; cpuid = PCPU_GET(cpuid); if (single_cpu && cpu != cpuid) { @@ -1435,11 +1439,11 @@ sched_4bsd_add(struct thread *td, int flags) } TD_SET_RUNQ(td); CTR2(KTR_RUNQ, "sched_add: adding td_sched:%p (td:%p) to runq", ts, td); - ts->ts_runq = &runq_global; + ts->ts_rqcpu = NOCPU; if ((td->td_flags & TDF_NOLOAD) == 0) sched_load_add(); - runq_add(ts->ts_runq, td, flags); + runq_add(TS_RUNQ_PTR(ts), td, flags); if (!maybe_preempt(td)) maybe_resched(td); if ((flags & SRQ_HOLDTD) == 0) @@ -1466,10 +1470,10 @@ sched_4bsd_rem(struct thread *td) if ((td->td_flags & TDF_NOLOAD) == 0) sched_load_rem(); #ifdef SMP - if (ts->ts_runq != &runq_global) - runq_length[ts->ts_runq - runq_pcpu]--; + if (ts->ts_rqcpu != NOCPU) + (*DPCPU_ID_PTR(ts->ts_rqcpu, runq_length))--; #endif - runq_remove(ts->ts_runq, td); + runq_remove(TS_RUNQ_PTR(ts), td); TD_SET_CAN_RUN(td); } @@ -1489,7 +1493,7 @@ sched_4bsd_choose(void) runq = &runq_global; td = runq_choose_fuzz(&runq_global, runq_fuzz); - tdcpu = runq_choose(&runq_pcpu[PCPU_GET(cpuid)]); + tdcpu = runq_choose(DPCPU_PTR(runq_pcpu)); if (td == NULL || (tdcpu != NULL && @@ -1497,7 +1501,7 @@ sched_4bsd_choose(void) CTR2(KTR_RUNQ, "choosing td %p from pcpu runq %d", tdcpu, PCPU_GET(cpuid)); td = tdcpu; - runq = &runq_pcpu[PCPU_GET(cpuid)]; + runq = DPCPU_PTR(runq_pcpu); } else { CTR1(KTR_RUNQ, "choosing td_sched %p from main runq", td); } @@ -1510,7 +1514,7 @@ sched_4bsd_choose(void) if (td) { #ifdef SMP if (td == tdcpu) - runq_length[PCPU_GET(cpuid)]--; + (*DPCPU_PTR(runq_length))--; #endif runq_remove(runq, td); td->td_flags |= TDF_DIDRUN; @@ -1561,7 +1565,7 @@ sched_4bsd_bind(struct thread *td, int cpu) td->td_flags |= TDF_BOUND; #ifdef SMP - ts->ts_runq = &runq_pcpu[cpu]; + ts->ts_rqcpu = cpu; if (PCPU_GET(cpuid) == cpu) return; @@ -1794,8 +1798,7 @@ sched_4bsd_affinity(struct thread *td) * If we are on a per-CPU runqueue that is in the set, * then nothing needs to be done. */ - if (ts->ts_runq != &runq_global && - THREAD_CAN_SCHED(td, ts->ts_runq - runq_pcpu)) + if (ts->ts_rqcpu != NOCPU && THREAD_CAN_SCHED(td, ts->ts_rqcpu)) return; /* Put this thread on a valid per-CPU runqueue. */home | help
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