sched/core: Disable SD_PREFER_SIBLING on asymmetric CPU capacity domains (9c63e84d) · Commits · 戴 / test

The 'prefer sibling' sched_domain flag is intended to encourage spreading tasks to sibling sched_domain to take advantage of more caches and core for SMT systems. It has recently been changed to be on all non-NUMA topology level. However, spreading across domains with CPU capacity asymmetry isn't desirable, e.g. spreading from high capacity to low capacity CPUs even if high capacity CPUs aren't overutilized might give access to more cache but the CPU will be slower and possibly lead to worse overall throughput. To prevent this, we need to remove SD_PREFER_SIBLING on the sched_domain level immediately below SD_ASYM_CPUCAPACITY. Signed-off-by:

Morten Rasmussen <morten.rasmussen@arm.com> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dietmar.eggemann@arm.com Cc: gaku.inami.xh@renesas.com Cc: valentin.schneider@arm.com Cc: vincent.guittot@linaro.org Link: http://lkml.kernel.org/r/1530699470-29808-13-git-send-email-morten.rasmussen@arm.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/sched/topology.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -1126,7 +1126,7 @@ sd_init(struct sched_domain_topology_level *tl,
		\| 0*SD_SHARE_CPUCAPACITY
		\| 0*SD_SHARE_PKG_RESOURCES
		\| 0*SD_SERIALIZE
		\| 0*SD_PREFER_SIBLING
		\| 1*SD_PREFER_SIBLING
		\| 0*SD_NUMA
		\| sd_flags
		,
		@@ -1152,17 +1152,21 @@ sd_init(struct sched_domain_topology_level *tl,
		if (sd->flags & SD_ASYM_CPUCAPACITY) {
		struct sched_domain *t = sd;

		/*
		* Don't attempt to spread across CPUs of different capacities.
		*/
		if (sd->child)
		sd->child->flags &= ~SD_PREFER_SIBLING;

		for_each_lower_domain(t)
		t->flags \|= SD_BALANCE_WAKE;
		}

		if (sd->flags & SD_SHARE_CPUCAPACITY) {
		sd->flags \|= SD_PREFER_SIBLING;
		sd->imbalance_pct = 110;
		sd->smt_gain = 1178; /* ~15% */

		} else if (sd->flags & SD_SHARE_PKG_RESOURCES) {
		sd->flags \|= SD_PREFER_SIBLING;
		sd->imbalance_pct = 117;
		sd->cache_nice_tries = 1;
		sd->busy_idx = 2;
		@@ -1173,6 +1177,7 @@ sd_init(struct sched_domain_topology_level *tl,
		sd->busy_idx = 3;
		sd->idle_idx = 2;

		sd->flags &= ~SD_PREFER_SIBLING;
		sd->flags \|= SD_SERIALIZE;
		if (sched_domains_numa_distance[tl->numa_level] > RECLAIM_DISTANCE) {
		sd->flags &= ~(SD_BALANCE_EXEC \|
		@@ -1182,7 +1187,6 @@ sd_init(struct sched_domain_topology_level *tl,

		#endif
		} else {
		sd->flags \|= SD_PREFER_SIBLING;
		sd->cache_nice_tries = 1;
		sd->busy_idx = 2;
		sd->idle_idx = 1;

Admin message