Re: [PATCH v8] perf: Sharing PMU counters across compatible events

Peter Zijlstra
2019-12-12T15:39:57Z

On Fri, Dec 06, 2019 at 04:24:47PM -0800, Song Liu wrote:

> @@ -2174,6 +2410,14 @@ __perf_remove_from_context(struct perf_event *event,
> update_cgrp_time_from_cpuctx(cpuctx);
> }
>
> + if (event->dup_master == event) {
> + if (ctx->is_active)
> + ctx_resched(cpuctx, cpuctx->task_ctx,
> + get_event_type(event), NULL, event);
> + else
> + perf_event_remove_dup(event, ctx);
> + }
> +
> event_sched_out(event, cpuctx, ctx);
> if (flags & DETACH_GROUP)
> perf_group_detach(event);
> @@ -2241,6 +2485,14 @@ static void __perf_event_disable(struct perf_event *event,
> update_cgrp_time_from_event(event);
> }
>
> + if (event->dup_master == event) {
> + if (ctx->is_active)
> + ctx_resched(cpuctx, cpuctx->task_ctx,
> + get_event_type(event), NULL, event);
> + else
> + perf_event_remove_dup(event, ctx);
> + }
> +
> if (event == event->group_leader)
> group_sched_out(event, cpuctx, ctx);
> else

> @@ -2544,7 +2793,9 @@ static void perf_event_sched_in(struct perf_cpu_context *cpuctx,
> */
> static void ctx_resched(struct perf_cpu_context *cpuctx,
> struct perf_event_context *task_ctx,
> - enum event_type_t event_type)
> + enum event_type_t event_type,
> + struct perf_event *event_add_dup,
> + struct perf_event *event_del_dup)
> {
> enum event_type_t ctx_event_type;
> bool cpu_event = !!(event_type & EVENT_CPU);
> @@ -2574,6 +2825,18 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
> else if (ctx_event_type & EVENT_PINNED)
> cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
>
> + if (event_add_dup) {
> + if (event_add_dup->ctx->is_active)
> + ctx_sched_out(event_add_dup->ctx, cpuctx, EVENT_ALL);
> + perf_event_setup_dup(event_add_dup, event_add_dup->ctx);
> + }
> +
> + if (event_del_dup) {
> + if (event_del_dup->ctx->is_active)
> + ctx_sched_out(event_del_dup->ctx, cpuctx, EVENT_ALL);
> + perf_event_remove_dup(event_del_dup, event_del_dup->ctx);
> + }
> +
> perf_event_sched_in(cpuctx, task_ctx, current);
> perf_pmu_enable(cpuctx->ctx.pmu);
> }

Yuck!

Why do you do a full reschedule when you take out a master?