A couple of scheduler tweaks which benchmark well for me:
- Add some simple SMT awareness. Try to keep as many different cores loaded up with jobs as possible before we start to make use of SMT. Have SMT "secondaries" function more as helpers to their respective primaries. This isn't enforced, it's an effort at herding/encouraging things to go in the right direction (for one because we support processor sets and those can be configured any way that you like). Seen at work with "top -1". - Don't allow sched_balance() to run any faster than the clock interrupt, because it causes terrible cache contention. Need to look into this in more detail because it's still not ideal.
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@ -1,4 +1,4 @@
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/* $NetBSD: kern_runq.c,v 1.53 2019/12/03 22:28:41 ad Exp $ */
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/* $NetBSD: kern_runq.c,v 1.54 2020/01/04 22:46:01 ad Exp $ */
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/*-
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* Copyright (c) 2019 The NetBSD Foundation, Inc.
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@ -56,7 +56,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: kern_runq.c,v 1.53 2019/12/03 22:28:41 ad Exp $");
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__KERNEL_RCSID(0, "$NetBSD: kern_runq.c,v 1.54 2020/01/04 22:46:01 ad Exp $");
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#include "opt_dtrace.h"
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@ -70,6 +70,7 @@ __KERNEL_RCSID(0, "$NetBSD: kern_runq.c,v 1.53 2019/12/03 22:28:41 ad Exp $");
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#include <sys/lwp.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/pset.h>
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#include <sys/sched.h>
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#include <sys/syscallargs.h>
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#include <sys/sysctl.h>
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@ -473,6 +474,18 @@ sched_takecpu(struct lwp *l)
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spc = &ci->ci_schedstate;
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eprio = lwp_eprio(l);
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/* If SMT primary is idle, send it back there. */
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tci = ci->ci_smt_primary;
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if ((tci->ci_schedstate.spc_flags & SPCF_IDLE) != 0 &&
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sched_migratable(l, tci)) {
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if (tci != ci) {
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spc->spc_ev_push.ev_count++;
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} else {
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spc->spc_ev_stay.ev_count++;
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}
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return tci;
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}
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/* Make sure that thread is in appropriate processor-set */
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if (__predict_true(spc->spc_psid == l->l_psid)) {
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/* If CPU of this thread is idling - run there */
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@ -520,16 +533,24 @@ sched_takecpu(struct lwp *l)
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/* Reached the end, start from the beginning. */
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next = cpu_lookup(0);
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}
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if (!sched_migratable(l, ci))
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continue;
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ici_spc = &ci->ci_schedstate;
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pri = MAX(ici_spc->spc_curpriority, ici_spc->spc_maxpriority);
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if (pri > lpri)
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continue;
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if (pri == lpri && spc->spc_count < ici_spc->spc_count)
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continue;
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if (pri == lpri) {
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/* Pick the least busy CPU. */
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if (spc->spc_count < ici_spc->spc_count)
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continue;
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if (!sched_migratable(l, ci))
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continue;
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/* Prefer SMT primaries over secondaries. */
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if ((ici_spc->spc_flags & SPCF_SMTPRIMARY) == 0 &&
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(spc->spc_flags & SPCF_SMTPRIMARY) != 0)
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continue;
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}
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lpri = pri;
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tci = ci;
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@ -552,12 +573,19 @@ sched_catchlwp(struct cpu_info *ci)
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struct schedstate_percpu *spc, *curspc;
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TAILQ_HEAD(, lwp) *q_head;
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struct lwp *l;
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bool smt;
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curspc = &curci->ci_schedstate;
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spc = &ci->ci_schedstate;
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KASSERT(curspc->spc_psid == spc->spc_psid);
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if (spc->spc_mcount < min_catch) {
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/*
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* Determine if the other CPU is our SMT twin. If it is, we'll be
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* more aggressive.
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*/
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smt = (curci->ci_package_id == ci->ci_package_id &&
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curci->ci_core_id == ci->ci_core_id);
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if ((!smt && spc->spc_mcount < min_catch) ||
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curspc->spc_psid != spc->spc_psid) {
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spc_unlock(ci);
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return NULL;
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}
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@ -576,9 +604,11 @@ sched_catchlwp(struct cpu_info *ci)
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l, (l->l_name ? l->l_name : l->l_proc->p_comm), l->l_stat);
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/* Look for threads, whose are allowed to migrate */
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if ((l->l_pflag & LP_BOUND) || lwp_cache_hot(l) ||
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if ((l->l_pflag & LP_BOUND) ||
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(!smt && lwp_cache_hot(l)) ||
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!sched_migratable(l, curci)) {
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l = TAILQ_NEXT(l, l_runq);
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/* XXX Gap: could walk down priority list. */
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continue;
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}
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@ -612,11 +642,25 @@ sched_catchlwp(struct cpu_info *ci)
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static void
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sched_balance(void *nocallout)
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{
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static int last __cacheline_aligned;
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struct cpu_info *ci, *hci;
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struct schedstate_percpu *spc;
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CPU_INFO_ITERATOR cii;
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u_int highest;
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u_int weight;
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int now;
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/*
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* Only one CPU at a time, no more than hz times per second. This
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* causes tremendous amount of cache misses otherwise.
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*/
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now = hardclock_ticks;
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if (atomic_load_relaxed(&last) == now) {
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return;
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}
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if (atomic_swap_uint(&last, now) == now) {
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return;
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}
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/* sanitize sysctl value */
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weight = MIN(average_weight, 100);
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@ -653,20 +697,16 @@ sched_balance(void *nocallout)
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}
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/*
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* Called from each CPU's idle loop.
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* Called from sched_idle() to handle migration.
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*/
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void
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sched_idle(void)
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static void
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sched_idle_migrate(void)
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{
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struct cpu_info *ci = curcpu(), *tci = NULL;
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struct schedstate_percpu *spc, *tspc;
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bool dlock = false;
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/* Check if there is a migrating LWP */
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spc = &ci->ci_schedstate;
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if (spc->spc_migrating == NULL)
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goto no_migration;
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spc_lock(ci);
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for (;;) {
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struct lwp *l;
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sched_resched_lwp(l, true);
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/* tci now unlocked */
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spc_unlock(ci);
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goto no_migration;
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return;
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}
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if (dlock == true) {
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KASSERT(tci != NULL);
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spc_unlock(tci);
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}
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spc_unlock(ci);
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}
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no_migration:
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/*
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* Called from each CPU's idle loop.
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*/
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void
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sched_idle(void)
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{
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struct cpu_info *ci = curcpu(), *tci = NULL;
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struct schedstate_percpu *spc, *tspc;
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lwp_t *l;
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spc = &ci->ci_schedstate;
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if (spc->spc_migrating != NULL) {
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sched_idle_migrate();
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}
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/* If this CPU is offline, or we have an LWP to run, we're done. */
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if ((spc->spc_flags & SPCF_OFFLINE) != 0 || spc->spc_count != 0) {
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return;
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}
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/* Reset the counter, and call the balancer */
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/* If we have SMT then help our siblings out. */
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tci = ci->ci_sibling[CPUREL_CORE];
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while (tci != ci) {
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tspc = &tci->ci_schedstate;
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if (tspc->spc_mcount != 0 && spc->spc_psid == tspc->spc_psid) {
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spc_dlock(ci, tci);
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l = sched_catchlwp(tci);
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spc_unlock(ci);
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if (l != NULL) {
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return;
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}
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}
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tci = tci->ci_sibling[CPUREL_CORE];
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}
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/* Reset the counter. */
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spc->spc_avgcount = 0;
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/* If an SMT secondary and in the default processor set, we're done. */
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if ((spc->spc_flags & SPCF_SMTPRIMARY) == 0 &&
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spc->spc_psid == PS_NONE) {
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return;
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}
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/* Call the balancer. */
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sched_balance(ci);
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tci = worker_ci;
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tspc = &tci->ci_schedstate;
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if (ci == tci || spc->spc_psid != tspc->spc_psid)
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return;
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/* Don't hit the locks unless there's something to do. */
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if (tspc->spc_mcount >= min_catch) {
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spc_dlock(ci, tci);
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