perf: Optimize context reschedule for single PMU cases

Currently re-scheduling a context will reschedule all active PMUs for
that context, even if it is known only a single event is added.

Namhyung reported that changing this to only reschedule the affected
PMU when possible provides significant performance gains under certain
conditions.

Therefore, allow partial context reschedules for a specific PMU, that
of the event modified.

While the patch looks somewhat noisy, it mostly just propagates a new
@pmu argument through the callchain and modifies the epc loop to only
pick the 'epc->pmu == @pmu' case.

Reported-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240807115549.920950699@infradead.org

diff --git a/kernel/events/core.c b/kernel/events/core.c
index c01a32687dad171a6517dfc4bc70bfdc5a32e8ba..dad2b9ac42c0b7a7b9778db0714ca20c1f68672f 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -685,30 +685,32 @@ do {                                                                      \
        ___p;                                                           \
 })
 
+#define for_each_epc(_epc, _ctx, _pmu, _cgroup)                                \
+       list_for_each_entry(_epc, &((_ctx)->pmu_ctx_list), pmu_ctx_entry) \
+               if (_cgroup && !_epc->nr_cgroups)                       \
+                       continue;                                       \
+               else if (_pmu && _epc->pmu != _pmu)                     \
+                       continue;                                       \
+               else
+
 static void perf_ctx_disable(struct perf_event_context *ctx, bool cgroup)
 {
        struct perf_event_pmu_context *pmu_ctx;
 
-       list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
-               if (cgroup && !pmu_ctx->nr_cgroups)
-                       continue;
+       for_each_epc(pmu_ctx, ctx, NULL, cgroup)
                perf_pmu_disable(pmu_ctx->pmu);
-       }
 }
 
 static void perf_ctx_enable(struct perf_event_context *ctx, bool cgroup)
 {
        struct perf_event_pmu_context *pmu_ctx;
 
-       list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
-               if (cgroup && !pmu_ctx->nr_cgroups)
-                       continue;
+       for_each_epc(pmu_ctx, ctx, NULL, cgroup)
                perf_pmu_enable(pmu_ctx->pmu);
-       }
 }
 
-static void ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type);
-static void ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type);
+static void ctx_sched_out(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t event_type);
+static void ctx_sched_in(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t event_type);
 
 #ifdef CONFIG_CGROUP_PERF
 
@@ -865,7 +867,7 @@ static void perf_cgroup_switch(struct task_struct *task)
        perf_ctx_lock(cpuctx, cpuctx->task_ctx);
        perf_ctx_disable(&cpuctx->ctx, true);
 
-       ctx_sched_out(&cpuctx->ctx, EVENT_ALL|EVENT_CGROUP);
+       ctx_sched_out(&cpuctx->ctx, NULL, EVENT_ALL|EVENT_CGROUP);
        /*
         * must not be done before ctxswout due
         * to update_cgrp_time_from_cpuctx() in
@@ -877,7 +879,7 @@ static void perf_cgroup_switch(struct task_struct *task)
         * perf_cgroup_set_timestamp() in ctx_sched_in()
         * to not have to pass task around
         */
-       ctx_sched_in(&cpuctx->ctx, EVENT_ALL|EVENT_CGROUP);
+       ctx_sched_in(&cpuctx->ctx, NULL, EVENT_ALL|EVENT_CGROUP);
 
        perf_ctx_enable(&cpuctx->ctx, true);
        perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
@@ -2656,7 +2658,8 @@ static void add_event_to_ctx(struct perf_event *event,
 }
 
 static void task_ctx_sched_out(struct perf_event_context *ctx,
-                               enum event_type_t event_type)
+                              struct pmu *pmu,
+                              enum event_type_t event_type)
 {
        struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
 
@@ -2666,18 +2669,19 @@ static void task_ctx_sched_out(struct perf_event_context *ctx,
        if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
                return;
 
-       ctx_sched_out(ctx, event_type);
+       ctx_sched_out(ctx, pmu, event_type);
 }
 
 static void perf_event_sched_in(struct perf_cpu_context *cpuctx,
-                               struct perf_event_context *ctx)
+                               struct perf_event_context *ctx,
+                               struct pmu *pmu)
 {
-       ctx_sched_in(&cpuctx->ctx, EVENT_PINNED);
+       ctx_sched_in(&cpuctx->ctx, pmu, EVENT_PINNED);
        if (ctx)
-                ctx_sched_in(ctx, EVENT_PINNED);
-       ctx_sched_in(&cpuctx->ctx, EVENT_FLEXIBLE);
+                ctx_sched_in(ctx, pmu, EVENT_PINNED);
+       ctx_sched_in(&cpuctx->ctx, pmu, EVENT_FLEXIBLE);
        if (ctx)
-                ctx_sched_in(ctx, EVENT_FLEXIBLE);
+                ctx_sched_in(ctx, pmu, EVENT_FLEXIBLE);
 }
 
 /*
@@ -2695,16 +2699,12 @@ static void perf_event_sched_in(struct perf_cpu_context *cpuctx,
  * event_type is a bit mask of the types of events involved. For CPU events,
  * event_type is only either EVENT_PINNED or EVENT_FLEXIBLE.
  */
-/*
- * XXX: ctx_resched() reschedule entire perf_event_context while adding new
- * event to the context or enabling existing event in the context. We can
- * probably optimize it by rescheduling only affected pmu_ctx.
- */
 static void ctx_resched(struct perf_cpu_context *cpuctx,
                        struct perf_event_context *task_ctx,
-                       enum event_type_t event_type)
+                       struct pmu *pmu, enum event_type_t event_type)
 {
        bool cpu_event = !!(event_type & EVENT_CPU);
+       struct perf_event_pmu_context *epc;
 
        /*
         * If pinned groups are involved, flexible groups also need to be
@@ -2715,10 +2715,14 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
 
        event_type &= EVENT_ALL;
 
-       perf_ctx_disable(&cpuctx->ctx, false);
+       for_each_epc(epc, &cpuctx->ctx, pmu, false)
+               perf_pmu_disable(epc->pmu);
+
        if (task_ctx) {
-               perf_ctx_disable(task_ctx, false);
-               task_ctx_sched_out(task_ctx, event_type);
+               for_each_epc(epc, task_ctx, pmu, false)
+                       perf_pmu_disable(epc->pmu);
+
+               task_ctx_sched_out(task_ctx, pmu, event_type);
        }
 
        /*
@@ -2729,15 +2733,19 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
         *  - otherwise, do nothing more.
         */
        if (cpu_event)
-               ctx_sched_out(&cpuctx->ctx, event_type);
+               ctx_sched_out(&cpuctx->ctx, pmu, event_type);
        else if (event_type & EVENT_PINNED)
-               ctx_sched_out(&cpuctx->ctx, EVENT_FLEXIBLE);
+               ctx_sched_out(&cpuctx->ctx, pmu, EVENT_FLEXIBLE);
+
+       perf_event_sched_in(cpuctx, task_ctx, pmu);
 
-       perf_event_sched_in(cpuctx, task_ctx);
+       for_each_epc(epc, &cpuctx->ctx, pmu, false)
+               perf_pmu_enable(epc->pmu);
 
-       perf_ctx_enable(&cpuctx->ctx, false);
-       if (task_ctx)
-               perf_ctx_enable(task_ctx, false);
+       if (task_ctx) {
+               for_each_epc(epc, task_ctx, pmu, false)
+                       perf_pmu_enable(epc->pmu);
+       }
 }
 
 void perf_pmu_resched(struct pmu *pmu)
@@ -2746,7 +2754,7 @@ void perf_pmu_resched(struct pmu *pmu)
        struct perf_event_context *task_ctx = cpuctx->task_ctx;
 
        perf_ctx_lock(cpuctx, task_ctx);
-       ctx_resched(cpuctx, task_ctx, EVENT_ALL|EVENT_CPU);
+       ctx_resched(cpuctx, task_ctx, pmu, EVENT_ALL|EVENT_CPU);
        perf_ctx_unlock(cpuctx, task_ctx);
 }
 
@@ -2802,9 +2810,10 @@ static int  __perf_install_in_context(void *info)
 #endif
 
        if (reprogram) {
-               ctx_sched_out(ctx, EVENT_TIME);
+               ctx_sched_out(ctx, NULL, EVENT_TIME);
                add_event_to_ctx(event, ctx);
-               ctx_resched(cpuctx, task_ctx, get_event_type(event));
+               ctx_resched(cpuctx, task_ctx, event->pmu_ctx->pmu,
+                           get_event_type(event));
        } else {
                add_event_to_ctx(event, ctx);
        }
@@ -2948,7 +2957,7 @@ static void __perf_event_enable(struct perf_event *event,
                return;
 
        if (ctx->is_active)
-               ctx_sched_out(ctx, EVENT_TIME);
+               ctx_sched_out(ctx, NULL, EVENT_TIME);
 
        perf_event_set_state(event, PERF_EVENT_STATE_INACTIVE);
        perf_cgroup_event_enable(event, ctx);
@@ -2957,7 +2966,7 @@ static void __perf_event_enable(struct perf_event *event,
                return;
 
        if (!event_filter_match(event)) {
-               ctx_sched_in(ctx, EVENT_TIME);
+               ctx_sched_in(ctx, NULL, EVENT_TIME);
                return;
        }
 
@@ -2966,7 +2975,7 @@ static void __perf_event_enable(struct perf_event *event,
         * then don't put it on unless the group is on.
         */
        if (leader != event && leader->state != PERF_EVENT_STATE_ACTIVE) {
-               ctx_sched_in(ctx, EVENT_TIME);
+               ctx_sched_in(ctx, NULL, EVENT_TIME);
                return;
        }
 
@@ -2974,7 +2983,7 @@ static void __perf_event_enable(struct perf_event *event,
        if (ctx->task)
                WARN_ON_ONCE(task_ctx != ctx);
 
-       ctx_resched(cpuctx, task_ctx, get_event_type(event));
+       ctx_resched(cpuctx, task_ctx, event->pmu_ctx->pmu, get_event_type(event));
 }
 
 /*
@@ -3276,8 +3285,17 @@ static void __pmu_ctx_sched_out(struct perf_event_pmu_context *pmu_ctx,
        perf_pmu_enable(pmu);
 }
 
+/*
+ * Be very careful with the @pmu argument since this will change ctx state.
+ * The @pmu argument works for ctx_resched(), because that is symmetric in
+ * ctx_sched_out() / ctx_sched_in() usage and the ctx state ends up invariant.
+ *
+ * However, if you were to be asymmetrical, you could end up with messed up
+ * state, eg. ctx->is_active cleared even though most EPCs would still actually
+ * be active.
+ */
 static void
-ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type)
+ctx_sched_out(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t event_type)
 {
        struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
        struct perf_event_pmu_context *pmu_ctx;
@@ -3331,11 +3349,8 @@ ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type)
 
        is_active ^= ctx->is_active; /* changed bits */
 
-       list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
-               if (cgroup && !pmu_ctx->nr_cgroups)
-                       continue;
+       for_each_epc(pmu_ctx, ctx, pmu, cgroup)
                __pmu_ctx_sched_out(pmu_ctx, is_active);
-       }
 }
 
 /*
@@ -3579,7 +3594,7 @@ unlock:
 
 inside_switch:
                perf_ctx_sched_task_cb(ctx, false);
-               task_ctx_sched_out(ctx, EVENT_ALL);
+               task_ctx_sched_out(ctx, NULL, EVENT_ALL);
 
                perf_ctx_enable(ctx, false);
                raw_spin_unlock(&ctx->lock);
@@ -3877,29 +3892,22 @@ static void pmu_groups_sched_in(struct perf_event_context *ctx,
                           merge_sched_in, &can_add_hw);
 }
 
-static void ctx_groups_sched_in(struct perf_event_context *ctx,
-                               struct perf_event_groups *groups,
-                               bool cgroup)
+static void __pmu_ctx_sched_in(struct perf_event_pmu_context *pmu_ctx,
+                              enum event_type_t event_type)
 {
-       struct perf_event_pmu_context *pmu_ctx;
-
-       list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
-               if (cgroup && !pmu_ctx->nr_cgroups)
-                       continue;
-               pmu_groups_sched_in(ctx, groups, pmu_ctx->pmu);
-       }
-}
+       struct perf_event_context *ctx = pmu_ctx->ctx;
 
-static void __pmu_ctx_sched_in(struct perf_event_context *ctx,
-                              struct pmu *pmu)
-{
-       pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu);
+       if (event_type & EVENT_PINNED)
+               pmu_groups_sched_in(ctx, &ctx->pinned_groups, pmu_ctx->pmu);
+       if (event_type & EVENT_FLEXIBLE)
+               pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu_ctx->pmu);
 }
 
 static void
-ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
+ctx_sched_in(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t event_type)
 {
        struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
+       struct perf_event_pmu_context *pmu_ctx;
        int is_active = ctx->is_active;
        bool cgroup = event_type & EVENT_CGROUP;
 
@@ -3935,12 +3943,16 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
         * First go through the list and put on any pinned groups
         * in order to give them the best chance of going on.
         */
-       if (is_active & EVENT_PINNED)
-               ctx_groups_sched_in(ctx, &ctx->pinned_groups, cgroup);
+       if (is_active & EVENT_PINNED) {
+               for_each_epc(pmu_ctx, ctx, pmu, cgroup)
+                       __pmu_ctx_sched_in(pmu_ctx, EVENT_PINNED);
+       }
 
        /* Then walk through the lower prio flexible groups */
-       if (is_active & EVENT_FLEXIBLE)
-               ctx_groups_sched_in(ctx, &ctx->flexible_groups, cgroup);
+       if (is_active & EVENT_FLEXIBLE) {
+               for_each_epc(pmu_ctx, ctx, pmu, cgroup)
+                       __pmu_ctx_sched_in(pmu_ctx, EVENT_FLEXIBLE);
+       }
 }
 
 static void perf_event_context_sched_in(struct task_struct *task)
@@ -3983,10 +3995,10 @@ static void perf_event_context_sched_in(struct task_struct *task)
         */
        if (!RB_EMPTY_ROOT(&ctx->pinned_groups.tree)) {
                perf_ctx_disable(&cpuctx->ctx, false);
-               ctx_sched_out(&cpuctx->ctx, EVENT_FLEXIBLE);
+               ctx_sched_out(&cpuctx->ctx, NULL, EVENT_FLEXIBLE);
        }
 
-       perf_event_sched_in(cpuctx, ctx);
+       perf_event_sched_in(cpuctx, ctx, NULL);
 
        perf_ctx_sched_task_cb(cpuctx->task_ctx, true);
 
@@ -4327,14 +4339,14 @@ static bool perf_rotate_context(struct perf_cpu_pmu_context *cpc)
                update_context_time(&cpuctx->ctx);
                __pmu_ctx_sched_out(cpu_epc, EVENT_FLEXIBLE);
                rotate_ctx(&cpuctx->ctx, cpu_event);
-               __pmu_ctx_sched_in(&cpuctx->ctx, pmu);
+               __pmu_ctx_sched_in(cpu_epc, EVENT_FLEXIBLE);
        }
 
        if (task_event)
                rotate_ctx(task_epc->ctx, task_event);
 
        if (task_event || (task_epc && cpu_event))
-               __pmu_ctx_sched_in(task_epc->ctx, pmu);
+               __pmu_ctx_sched_in(task_epc, EVENT_FLEXIBLE);
 
        perf_pmu_enable(pmu);
        perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
@@ -4400,7 +4412,7 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx)
 
        cpuctx = this_cpu_ptr(&perf_cpu_context);
        perf_ctx_lock(cpuctx, ctx);
-       ctx_sched_out(ctx, EVENT_TIME);
+       ctx_sched_out(ctx, NULL, EVENT_TIME);
 
        list_for_each_entry(event, &ctx->event_list, event_entry) {
                enabled |= event_enable_on_exec(event, ctx);
@@ -4412,9 +4424,9 @@ static void perf_event_enable_on_exec(struct perf_event_context *ctx)
         */
        if (enabled) {
                clone_ctx = unclone_ctx(ctx);
-               ctx_resched(cpuctx, ctx, event_type);
+               ctx_resched(cpuctx, ctx, NULL, event_type);
        } else {
-               ctx_sched_in(ctx, EVENT_TIME);
+               ctx_sched_in(ctx, NULL, EVENT_TIME);
        }
        perf_ctx_unlock(cpuctx, ctx);
 
@@ -13202,7 +13214,7 @@ static void perf_event_exit_task_context(struct task_struct *child)
         * in.
         */
        raw_spin_lock_irq(&child_ctx->lock);
-       task_ctx_sched_out(child_ctx, EVENT_ALL);
+       task_ctx_sched_out(child_ctx, NULL, EVENT_ALL);
 
        /*
         * Now that the context is inactive, destroy the task <-> ctx relation
@@ -13751,7 +13763,7 @@ static void __perf_event_exit_context(void *__info)
        struct perf_event *event;
 
        raw_spin_lock(&ctx->lock);
-       ctx_sched_out(ctx, EVENT_TIME);
+       ctx_sched_out(ctx, NULL, EVENT_TIME);
        list_for_each_entry(event, &ctx->event_list, event_entry)
                __perf_remove_from_context(event, cpuctx, ctx, (void *)DETACH_GROUP);
        raw_spin_unlock(&ctx->lock);