Date: Thu, 29 Jul 2021 02:00:33 GMT From: Alexander Motin <mav@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: aefe0a8c32d3 - main - Refactor/optimize cpu_search_*(). Message-ID: <202107290200.16T20XOM038857@gitrepo.freebsd.org>
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The branch main has been updated by mav: URL: https://cgit.FreeBSD.org/src/commit/?id=aefe0a8c32d370f2fdd0d0771eb59f8845beda17 commit aefe0a8c32d370f2fdd0d0771eb59f8845beda17 Author: Alexander Motin <mav@FreeBSD.org> AuthorDate: 2021-07-29 01:18:50 +0000 Commit: Alexander Motin <mav@FreeBSD.org> CommitDate: 2021-07-29 02:00:29 +0000 Refactor/optimize cpu_search_*(). Remove cpu_search_both(), unused for many years. Without it there is less sense for the trick of compiling common cpu_search() into separate cpu_search_lowest() and cpu_search_highest(), so split them completely, making code more readable. While there, split iteration over children groups and CPUs, complicating code for very small deduplication. Stop passing cpuset_t arguments by value and avoid some manipulations. Since MAXCPU bump from 64 to 256, what was a single register turned into 32-byte memory array, requiring memory allocation and accesses. Splitting struct cpu_search into parameter and result parts allows to even more reduce stack usage, since the first can be passed through on recursion. Remove CPU_FFS() from the hot paths, precalculating first and last CPU for each CPU group in advance during initialization. Again, it was not a problem for 64 CPUs before, but for 256 FFS needs much more code. With these changes on 80-thread system doing ~260K uncached ZFS reads per second I observe ~30% reduction of time spent in cpu_search_*(). MFC after: 1 month --- sys/kern/sched_ule.c | 290 +++++++++++++++++++++------------------------------ sys/kern/subr_smp.c | 12 +++ sys/sys/smp.h | 2 + 3 files changed, 134 insertions(+), 170 deletions(-) diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c index 094a3fffef8c..3bb73d64a70c 100644 --- a/sys/kern/sched_ule.c +++ b/sys/kern/sched_ule.c @@ -631,170 +631,120 @@ sched_random(void) } struct cpu_search { - cpuset_t cs_mask; + cpuset_t *cs_mask; u_int cs_prefer; int cs_pri; /* Min priority for low. */ int cs_limit; /* Max load for low, min load for high. */ +}; + +struct cpu_search_res { int cs_cpu; int cs_load; }; -#define CPU_SEARCH_LOWEST 0x1 -#define CPU_SEARCH_HIGHEST 0x2 -#define CPU_SEARCH_BOTH (CPU_SEARCH_LOWEST|CPU_SEARCH_HIGHEST) - -static __always_inline int cpu_search(const struct cpu_group *cg, - struct cpu_search *low, struct cpu_search *high, const int match); -int __noinline cpu_search_lowest(const struct cpu_group *cg, - struct cpu_search *low); -int __noinline cpu_search_highest(const struct cpu_group *cg, - struct cpu_search *high); -int __noinline cpu_search_both(const struct cpu_group *cg, - struct cpu_search *low, struct cpu_search *high); - -/* - * Search the tree of cpu_groups for the lowest or highest loaded cpu - * according to the match argument. This routine actually compares the - * load on all paths through the tree and finds the least loaded cpu on - * the least loaded path, which may differ from the least loaded cpu in - * the system. This balances work among caches and buses. - * - * This inline is instantiated in three forms below using constants for the - * match argument. It is reduced to the minimum set for each case. It is - * also recursive to the depth of the tree. - */ -static __always_inline int -cpu_search(const struct cpu_group *cg, struct cpu_search *low, - struct cpu_search *high, const int match) -{ - struct cpu_search lgroup; - struct cpu_search hgroup; - cpuset_t cpumask; - struct cpu_group *child; +/* + * Search the tree of cpu_groups for the lowest or highest loaded CPU. + * These routines actually compare the load on all paths through the tree + * and find the least loaded cpu on the least loaded path, which may differ + * from the least loaded cpu in the system. This balances work among caches + * and buses. + */ +static int +cpu_search_lowest(const struct cpu_group *cg, const struct cpu_search *s, + struct cpu_search_res *r) +{ + struct cpu_search_res lr; struct tdq *tdq; - int cpu, i, hload, lload, load, total, rnd; + int c, bload, l, load, total; total = 0; - cpumask = cg->cg_mask; - if (match & CPU_SEARCH_LOWEST) { - lload = INT_MAX; - lgroup = *low; - } - if (match & CPU_SEARCH_HIGHEST) { - hload = INT_MIN; - hgroup = *high; - } + bload = INT_MAX; + r->cs_cpu = -1; - /* Iterate through the child CPU groups and then remaining CPUs. */ - for (i = cg->cg_children, cpu = mp_maxid; ; ) { - if (i == 0) { -#ifdef HAVE_INLINE_FFSL - cpu = CPU_FFS(&cpumask) - 1; -#else - while (cpu >= 0 && !CPU_ISSET(cpu, &cpumask)) - cpu--; -#endif - if (cpu < 0) - break; - child = NULL; - } else - child = &cg->cg_child[i - 1]; - - if (match & CPU_SEARCH_LOWEST) - lgroup.cs_cpu = -1; - if (match & CPU_SEARCH_HIGHEST) - hgroup.cs_cpu = -1; - if (child) { /* Handle child CPU group. */ - CPU_ANDNOT(&cpumask, &child->cg_mask); - switch (match) { - case CPU_SEARCH_LOWEST: - load = cpu_search_lowest(child, &lgroup); - break; - case CPU_SEARCH_HIGHEST: - load = cpu_search_highest(child, &hgroup); - break; - case CPU_SEARCH_BOTH: - load = cpu_search_both(child, &lgroup, &hgroup); - break; - } - } else { /* Handle child CPU. */ - CPU_CLR(cpu, &cpumask); - tdq = TDQ_CPU(cpu); - load = tdq->tdq_load * 256; - rnd = sched_random() % 32; - if (match & CPU_SEARCH_LOWEST) { - if (cpu == low->cs_prefer) - load -= 64; - /* If that CPU is allowed and get data. */ - if (tdq->tdq_lowpri > lgroup.cs_pri && - tdq->tdq_load <= lgroup.cs_limit && - CPU_ISSET(cpu, &lgroup.cs_mask)) { - lgroup.cs_cpu = cpu; - lgroup.cs_load = load - rnd; - } + /* Loop through children CPU groups if there are any. */ + if (cg->cg_children > 0) { + for (c = cg->cg_children - 1; c >= 0; c--) { + load = cpu_search_lowest(&cg->cg_child[c], s, &lr); + total += load; + if (lr.cs_cpu >= 0 && (load < bload || + (load == bload && lr.cs_load < r->cs_load))) { + bload = load; + r->cs_cpu = lr.cs_cpu; + r->cs_load = lr.cs_load; } - if (match & CPU_SEARCH_HIGHEST) - if (tdq->tdq_load >= hgroup.cs_limit && - tdq->tdq_transferable && - CPU_ISSET(cpu, &hgroup.cs_mask)) { - hgroup.cs_cpu = cpu; - hgroup.cs_load = load - rnd; - } } - total += load; + return (total); + } - /* We have info about child item. Compare it. */ - if (match & CPU_SEARCH_LOWEST) { - if (lgroup.cs_cpu >= 0 && - (load < lload || - (load == lload && lgroup.cs_load < low->cs_load))) { - lload = load; - low->cs_cpu = lgroup.cs_cpu; - low->cs_load = lgroup.cs_load; - } - } - if (match & CPU_SEARCH_HIGHEST) - if (hgroup.cs_cpu >= 0 && - (load > hload || - (load == hload && hgroup.cs_load > high->cs_load))) { - hload = load; - high->cs_cpu = hgroup.cs_cpu; - high->cs_load = hgroup.cs_load; - } - if (child) { - i--; - if (i == 0 && CPU_EMPTY(&cpumask)) - break; + /* Loop through children CPUs otherwise. */ + for (c = cg->cg_last; c >= cg->cg_first; c--) { + if (!CPU_ISSET(c, &cg->cg_mask)) + continue; + tdq = TDQ_CPU(c); + l = tdq->tdq_load; + load = l * 256; + if (c == s->cs_prefer) + load -= 128; + total += load; + if (l > s->cs_limit || tdq->tdq_lowpri <= s->cs_pri || + !CPU_ISSET(c, s->cs_mask)) + continue; + load -= sched_random() % 128; + if (load < bload) { + bload = load; + r->cs_cpu = c; } -#ifndef HAVE_INLINE_FFSL - else - cpu--; -#endif } + r->cs_load = bload; return (total); } -/* - * cpu_search instantiations must pass constants to maintain the inline - * optimization. - */ -int -cpu_search_lowest(const struct cpu_group *cg, struct cpu_search *low) +static int +cpu_search_highest(const struct cpu_group *cg, const struct cpu_search *s, + struct cpu_search_res *r) { - return cpu_search(cg, low, NULL, CPU_SEARCH_LOWEST); -} + struct cpu_search_res lr; + struct tdq *tdq; + int c, bload, l, load, total; -int -cpu_search_highest(const struct cpu_group *cg, struct cpu_search *high) -{ - return cpu_search(cg, NULL, high, CPU_SEARCH_HIGHEST); -} + total = 0; + bload = INT_MIN; + r->cs_cpu = -1; -int -cpu_search_both(const struct cpu_group *cg, struct cpu_search *low, - struct cpu_search *high) -{ - return cpu_search(cg, low, high, CPU_SEARCH_BOTH); + /* Loop through children CPU groups if there are any. */ + if (cg->cg_children > 0) { + for (c = cg->cg_children - 1; c >= 0; c--) { + load = cpu_search_highest(&cg->cg_child[c], s, &lr); + total += load; + if (lr.cs_cpu >= 0 && (load > bload || + (load == bload && lr.cs_load > r->cs_load))) { + bload = load; + r->cs_cpu = lr.cs_cpu; + r->cs_load = lr.cs_load; + } + } + return (total); + } + + /* Loop through children CPUs otherwise. */ + for (c = cg->cg_last; c >= cg->cg_first; c--) { + if (!CPU_ISSET(c, &cg->cg_mask)) + continue; + tdq = TDQ_CPU(c); + l = tdq->tdq_load; + load = l * 256; + total += load; + if (l < s->cs_limit || !tdq->tdq_transferable || + !CPU_ISSET(c, s->cs_mask)) + continue; + load -= sched_random() % 128; + if (load > bload) { + bload = load; + r->cs_cpu = c; + } + } + r->cs_load = bload; + return (total); } /* @@ -803,33 +753,33 @@ cpu_search_both(const struct cpu_group *cg, struct cpu_search *low, * acceptable. */ static inline int -sched_lowest(const struct cpu_group *cg, cpuset_t mask, int pri, int maxload, +sched_lowest(const struct cpu_group *cg, cpuset_t *mask, int pri, int maxload, int prefer) { - struct cpu_search low; + struct cpu_search s; + struct cpu_search_res r; - low.cs_cpu = -1; - low.cs_prefer = prefer; - low.cs_mask = mask; - low.cs_pri = pri; - low.cs_limit = maxload; - cpu_search_lowest(cg, &low); - return low.cs_cpu; + s.cs_prefer = prefer; + s.cs_mask = mask; + s.cs_pri = pri; + s.cs_limit = maxload; + cpu_search_lowest(cg, &s, &r); + return (r.cs_cpu); } /* * Find the cpu with the highest load via the highest loaded path. */ static inline int -sched_highest(const struct cpu_group *cg, cpuset_t mask, int minload) +sched_highest(const struct cpu_group *cg, cpuset_t *mask, int minload) { - struct cpu_search high; + struct cpu_search s; + struct cpu_search_res r; - high.cs_cpu = -1; - high.cs_mask = mask; - high.cs_limit = minload; - cpu_search_highest(cg, &high); - return high.cs_cpu; + s.cs_mask = mask; + s.cs_limit = minload; + cpu_search_highest(cg, &s, &r); + return (r.cs_cpu); } static void @@ -841,7 +791,7 @@ sched_balance_group(struct cpu_group *cg) CPU_FILL(&hmask); for (;;) { - high = sched_highest(cg, hmask, 2); + high = sched_highest(cg, &hmask, 2); /* Stop if there is no more CPU with transferrable threads. */ if (high == -1) break; @@ -853,7 +803,7 @@ sched_balance_group(struct cpu_group *cg) anylow = 1; tdq = TDQ_CPU(high); nextlow: - low = sched_lowest(cg, lmask, -1, tdq->tdq_load - 1, high); + low = sched_lowest(cg, &lmask, -1, tdq->tdq_load - 1, high); /* Stop if we looked well and found no less loaded CPU. */ if (anylow && low == -1) break; @@ -995,7 +945,7 @@ tdq_idled(struct tdq *tdq) restart: switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt; for (cg = tdq->tdq_cg; ; ) { - cpu = sched_highest(cg, mask, steal_thresh); + cpu = sched_highest(cg, &mask, steal_thresh); /* * We were assigned a thread but not preempted. Returning * 0 here will cause our caller to switch to it. @@ -1244,7 +1194,7 @@ sched_pickcpu(struct thread *td, int flags) struct cpu_group *cg, *ccg; struct td_sched *ts; struct tdq *tdq; - cpuset_t mask; + cpuset_t *mask; int cpu, pri, self, intr; self = PCPU_GET(cpuid); @@ -1287,14 +1237,14 @@ sched_pickcpu(struct thread *td, int flags) SCHED_AFFINITY(ts, CG_SHARE_L2)) { if (cg->cg_flags & CG_FLAG_THREAD) { /* Check all SMT threads for being idle. */ - for (cpu = CPU_FFS(&cg->cg_mask) - 1; ; cpu++) { + for (cpu = cg->cg_first; cpu <= cg->cg_last; cpu++) { if (CPU_ISSET(cpu, &cg->cg_mask) && TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE) break; - if (cpu >= mp_maxid) { - SCHED_STAT_INC(pickcpu_idle_affinity); - return (ts->ts_cpu); - } + } + if (cpu > cg->cg_last) { + SCHED_STAT_INC(pickcpu_idle_affinity); + return (ts->ts_cpu); } } else { SCHED_STAT_INC(pickcpu_idle_affinity); @@ -1321,7 +1271,7 @@ llc: if (ccg == cpu_top) ccg = NULL; cpu = -1; - mask = td->td_cpuset->cs_mask; + mask = &td->td_cpuset->cs_mask; pri = td->td_priority; /* * Try hard to keep interrupts within found LLC. Search the LLC for @@ -1931,7 +1881,7 @@ tdq_trysteal(struct tdq *tdq) spinlock_enter(); TDQ_UNLOCK(tdq); for (i = 1, cg = tdq->tdq_cg; ; ) { - cpu = sched_highest(cg, mask, steal_thresh); + cpu = sched_highest(cg, &mask, steal_thresh); /* * If a thread was added while interrupts were disabled don't * steal one here. @@ -3002,7 +2952,7 @@ sysctl_kern_sched_topology_spec_internal(struct sbuf *sb, struct cpu_group *cg, sbuf_printf(sb, "%*s <cpu count=\"%d\" mask=\"%s\">", indent, "", cg->cg_count, cpusetobj_strprint(cpusetbuf, &cg->cg_mask)); first = TRUE; - for (i = 0; i < MAXCPU; i++) { + for (i = cg->cg_first; i <= cg->cg_last; i++) { if (CPU_ISSET(i, &cg->cg_mask)) { if (!first) sbuf_printf(sb, ", "); diff --git a/sys/kern/subr_smp.c b/sys/kern/subr_smp.c index 935fb6ee977c..bfe890d773f9 100644 --- a/sys/kern/subr_smp.c +++ b/sys/kern/subr_smp.c @@ -630,6 +630,17 @@ smp_rendezvous(void (* setup_func)(void *), static struct cpu_group group[MAXCPU * MAX_CACHE_LEVELS + 1]; +static void +smp_topo_fill(struct cpu_group *cg) +{ + int c; + + for (c = 0; c < cg->cg_children; c++) + smp_topo_fill(&cg->cg_child[c]); + cg->cg_first = CPU_FFS(&cg->cg_mask) - 1; + cg->cg_last = CPU_FLS(&cg->cg_mask) - 1; +} + struct cpu_group * smp_topo(void) { @@ -693,6 +704,7 @@ smp_topo(void) top = &top->cg_child[0]; top->cg_parent = NULL; } + smp_topo_fill(top); return (top); } diff --git a/sys/sys/smp.h b/sys/sys/smp.h index a971ffbbd91b..cee1199015a7 100644 --- a/sys/sys/smp.h +++ b/sys/sys/smp.h @@ -81,6 +81,8 @@ struct cpu_group { struct cpu_group *cg_child; /* Optional children groups. */ cpuset_t cg_mask; /* Mask of cpus in this group. */ int32_t cg_count; /* Count of cpus in this group. */ + int32_t cg_first; /* First cpu in this group. */ + int32_t cg_last; /* Last cpu in this group. */ int16_t cg_children; /* Number of children groups. */ int8_t cg_level; /* Shared cache level. */ int8_t cg_flags; /* Traversal modifiers. */
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