linux-kernel - Re: [PATCH 02/14] perf/x86: output NMI overhead

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Date:   Thu, 24 Nov 2016 20:02:42 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     kan.liang@...el.com, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, alexander.shishkin@...ux.intel.com,
        tglx@...utronix.de, namhyung@...nel.org, jolsa@...nel.org,
        adrian.hunter@...el.com, wangnan0@...wei.com, andi@...stfloor.org
Subject: Re: [PATCH 02/14] perf/x86: output NMI overhead

On Thu, Nov 24, 2016 at 04:19:09PM +0000, Mark Rutland wrote:
> >  static void
> >  event_sched_out(struct perf_event *event,
> >  		  struct perf_cpu_context *cpuctx,
> > -		  struct perf_event_context *ctx)
> > +		  struct perf_event_context *ctx,
> > +		  bool log_overhead)
> 
> Boolean parameter are always confusing. Why not pass the flags directly? That
> way we can pass *which* overhead to log, and make the callsites easier to
> understand.
> 
> >  	event->tstamp_stopped = tstamp;
> > -	event->pmu->del(event, 0);
> > +	event->pmu->del(event, log_overhead ? PERF_EF_LOG : 0);
> 
> ... which we could pass on here.
> 
> > @@ -1835,20 +1835,21 @@ event_sched_out(struct perf_event *event,
> >  static void
> >  group_sched_out(struct perf_event *group_event,
> >  		struct perf_cpu_context *cpuctx,
> > -		struct perf_event_context *ctx)
> > +		struct perf_event_context *ctx,
> > +		bool log_overhead)
> 
> Likewise.
> 
> > @@ -1872,7 +1873,7 @@ __perf_remove_from_context(struct perf_event *event,
> >  {
> >  	unsigned long flags = (unsigned long)info;
> >  
> > -	event_sched_out(event, cpuctx, ctx);
> > +	event_sched_out(event, cpuctx, ctx, false);
> >  	if (flags & DETACH_GROUP)
> >  		perf_group_detach(event);
> >  	list_del_event(event, ctx);
> > @@ -1918,9 +1919,9 @@ static void __perf_event_disable(struct perf_event *event,
> >  	update_cgrp_time_from_event(event);
> >  	update_group_times(event);
> >  	if (event == event->group_leader)
> > -		group_sched_out(event, cpuctx, ctx);
> > +		group_sched_out(event, cpuctx, ctx, true);
> >  	else
> > -		event_sched_out(event, cpuctx, ctx);
> > +		event_sched_out(event, cpuctx, ctx, true);
> 
> Why does this differ from __perf_remove_from_context()?

So I'm not a great fan of sprinkling all this through the core code at
all.