From 8d5bce0c37fa10f21dbdd6a6d8fcba85202fe24e Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 9 Mar 2018 14:56:27 +0100 Subject: [PATCH] perf/core: Optimize perf_rotate_context() event scheduling The event schedule order (as per perf_event_sched_in()) is: - cpu pinned - task pinned - cpu flexible - task flexible But perf_rotate_context() will unschedule cpu-flexible even if it doesn't need a rotation. Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- kernel/events/core.c | 60 +++++++++++++++++++++++++++----------------- 1 file changed, 37 insertions(+), 23 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 460e485220e8..f98c0f88cc94 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -430,7 +430,7 @@ static void update_perf_cpu_limits(void) WRITE_ONCE(perf_sample_allowed_ns, tmp); } -static int perf_rotate_context(struct perf_cpu_context *cpuctx); +static bool perf_rotate_context(struct perf_cpu_context *cpuctx); int perf_proc_update_handler(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, @@ -1041,7 +1041,7 @@ list_update_cgroup_event(struct perf_event *event, static enum hrtimer_restart perf_mux_hrtimer_handler(struct hrtimer *hr) { struct perf_cpu_context *cpuctx; - int rotations = 0; + bool rotations; lockdep_assert_irqs_disabled(); @@ -3600,52 +3600,66 @@ static void rotate_ctx(struct perf_event_context *ctx, struct perf_event *event) perf_event_groups_insert(&ctx->flexible_groups, event); } -static int perf_rotate_context(struct perf_cpu_context *cpuctx) +static inline struct perf_event * +ctx_first_active(struct perf_event_context *ctx) { - struct perf_event *ctx_event = NULL, *cpuctx_event = NULL; + return list_first_entry_or_null(&ctx->flexible_active, + struct perf_event, active_list); +} + +static bool perf_rotate_context(struct perf_cpu_context *cpuctx) +{ + struct perf_event *cpu_event = NULL, *task_event = NULL; + bool cpu_rotate = false, task_rotate = false; struct perf_event_context *ctx = NULL; - int rotate = 0; + + /* + * Since we run this from IRQ context, nobody can install new + * events, thus the event count values are stable. + */ if (cpuctx->ctx.nr_events) { if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active) - rotate = 1; + cpu_rotate = true; } ctx = cpuctx->task_ctx; if (ctx && ctx->nr_events) { if (ctx->nr_events != ctx->nr_active) - rotate = 1; + task_rotate = true; } - if (!rotate) - goto done; + if (!(cpu_rotate || task_rotate)) + return false; perf_ctx_lock(cpuctx, cpuctx->task_ctx); perf_pmu_disable(cpuctx->ctx.pmu); - cpuctx_event = list_first_entry_or_null(&cpuctx->ctx.flexible_active, - struct perf_event, active_list); - if (ctx) { - ctx_event = list_first_entry_or_null(&ctx->flexible_active, - struct perf_event, active_list); - } + if (task_rotate) + task_event = ctx_first_active(ctx); + if (cpu_rotate) + cpu_event = ctx_first_active(&cpuctx->ctx); - cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE); - if (ctx) + /* + * As per the order given at ctx_resched() first 'pop' task flexible + * and then, if needed CPU flexible. + */ + if (task_event || (ctx && cpu_event)) ctx_sched_out(ctx, cpuctx, EVENT_FLEXIBLE); + if (cpu_event) + cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE); - if (cpuctx_event) - rotate_ctx(&cpuctx->ctx, cpuctx_event); - if (ctx_event) - rotate_ctx(ctx, ctx_event); + if (task_event) + rotate_ctx(ctx, task_event); + if (cpu_event) + rotate_ctx(&cpuctx->ctx, cpu_event); perf_event_sched_in(cpuctx, ctx, current); perf_pmu_enable(cpuctx->ctx.pmu); perf_ctx_unlock(cpuctx, cpuctx->task_ctx); -done: - return rotate; + return true; } void perf_event_task_tick(void)