linux-kernel - Re: [PATCH 4/5] perf: Add context time freeze

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Message-ID: <20240807190921.GE31338@noisy.programming.kicks-ass.net>
Date: Wed, 7 Aug 2024 21:09:21 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: mingo@...nel.org, acme@...nel.org, namhyung@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] perf: Add context time freeze

On Wed, Aug 07, 2024 at 11:17:18AM -0400, Liang, Kan wrote:

> > +static inline void __perf_ctx_unlock(struct perf_event_context *ctx)
> > +{
> > +	/*
> > +	 * If ctx_sched_in() didn't again set any ALL flags, clean up
> > +	 * after ctx_sched_out() by clearing is_active.
> > +	 */
> > +	if (ctx->is_active & EVENT_FROZEN) {
> > +		if (!(ctx->is_active & EVENT_ALL))
> 
> Nit:
> It may be better to add a macro/inline function to replace all the
> (ctx->is_active & EVENT_ALL) check? For example,
> 
> +static inline bool perf_ctx_has_active_events(struct perf_event_context
> *ctx)
> +{
> +	return ctx->is_active & EVENT_ALL;
> +}
> ...
> +	if (ctx->is_active & EVENT_FROZEN) {
> +		if (!perf_ctx_has_active_events(ctx))
> +			ctx->is_active = 0;
> +		else
> +			ctx->is_active &= ~EVENT_FROZEN;
> 
> It can tell very straightforwardly that we want to clear all flags if
> there is no active event.
> The EVENT_ALL may bring confusion. It actually means all events, not all
> event types. The developer may have to go to the define and figure out
> what exactly the EVENT_ALL includes.

I'll push this on the todo list. I'm running short of time before I'm
taking a holiday and need to also spend time looking at the sched_ext
thing.