From c4fba1161bf28c8ac972f4526b46f7f40fa8d515 Mon Sep 17 00:00:00 2001 From: Dario Faggioli Date: Tue, 17 Jan 2017 18:27:03 +0100 Subject: [PATCH] xen: sched: impove use of cpumask scratch space in Credit1. It is ok to use just cpumask_scratch in csched_runq_steal(). In fact, the cpu parameter comes from the cpu local variable in csched_load_balance(), which in turn comes from cpu in csched_schedule(), which is smp_processor_id(). While there, also: - move the comment about cpumask_scratch in the header where the scratch space is declared; - spell more clearly (in that same comment) what are the serialization rules. No functional change intended. Signed-off-by: Dario Faggioli Acked-by: George Dunlap --- xen/common/sched_credit.c | 5 ++--- xen/common/schedule.c | 7 +------ xen/include/xen/sched-if.h | 7 +++++++ 3 files changed, 10 insertions(+), 9 deletions(-) diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c index dfe8545800..ad2081919e 100644 --- a/xen/common/sched_credit.c +++ b/xen/common/sched_credit.c @@ -1636,9 +1636,8 @@ csched_runq_steal(int peer_cpu, int cpu, int pri, int balance_step) && !__vcpu_has_soft_affinity(vc, vc->cpu_hard_affinity) ) continue; - csched_balance_cpumask(vc, balance_step, cpumask_scratch_cpu(cpu)); - if ( __csched_vcpu_is_migrateable(vc, cpu, - cpumask_scratch_cpu(cpu)) ) + csched_balance_cpumask(vc, balance_step, cpumask_scratch); + if ( __csched_vcpu_is_migrateable(vc, cpu, cpumask_scratch) ) { /* We got a candidate. Grab it! */ TRACE_3D(TRC_CSCHED_STOLEN_VCPU, peer_cpu, diff --git a/xen/common/schedule.c b/xen/common/schedule.c index 36ff2e93c4..bee5d1fa34 100644 --- a/xen/common/schedule.c +++ b/xen/common/schedule.c @@ -65,12 +65,7 @@ static void poll_timer_fn(void *data); DEFINE_PER_CPU(struct schedule_data, schedule_data); DEFINE_PER_CPU(struct scheduler *, scheduler); -/* - * Scratch space, for avoiding having too many cpumask_var_t on the stack. - * Properly serializing access, if necessary, is responsibility of each - * scheduler (typically, one can expect this to be protected by the per pCPU - * or per runqueue lock). - */ +/* Scratch space for cpumasks. */ DEFINE_PER_CPU(cpumask_t, cpumask_scratch); extern const struct scheduler *__start_schedulers_array[], *__end_schedulers_array[]; diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h index bc0e794b0f..c32ee7ae38 100644 --- a/xen/include/xen/sched-if.h +++ b/xen/include/xen/sched-if.h @@ -47,6 +47,13 @@ DECLARE_PER_CPU(struct schedule_data, schedule_data); DECLARE_PER_CPU(struct scheduler *, scheduler); DECLARE_PER_CPU(struct cpupool *, cpupool); +/* + * Scratch space, for avoiding having too many cpumask_t on the stack. + * Within each scheduler, when using the scratch mask of one pCPU: + * - the pCPU must belong to the scheduler, + * - the caller must own the per-pCPU scheduler lock (a.k.a. runqueue + * lock). + */ DECLARE_PER_CPU(cpumask_t, cpumask_scratch); #define cpumask_scratch (&this_cpu(cpumask_scratch)) #define cpumask_scratch_cpu(c) (&per_cpu(cpumask_scratch, c)) -- 2.30.2