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

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Date:   Thu, 12 Dec 2019 16:39:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v8] perf: Sharing PMU counters across compatible events

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?