linux-kernel - Re: [tip:perf/core] perf/core: Check return value of the perf_event

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Message-ID: <20160830064724.GX10153@twins.programming.kicks-ass.net>
Date:   Tue, 30 Aug 2016 08:47:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Vegard Nossum <vegard.nossum@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephane Eranian <eranian@...gle.com>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Ingo Molnar <mingo@...nel.org>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kan Liang <kan.liang@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf/core: Check return value of the
 perf_event_read() IPI

On Mon, Aug 29, 2016 at 08:58:41PM +0200, Jiri Olsa wrote:
> couldn't we just call smp_call_function_single(cpu_to_read, __perf_event_read, ...
> once we read oncpu != -1 ?
> 

Yes, and at that point we can simply revert this WARN, because that is
exactly the same.

Which I think is what I'm going to do.

If oncpu is not valid, the sched_out that made it invalid will have
updated the event count and we're good.

All I'll leave is an explicit comment that we've ignored the
smp_call_function_single() return value on purpose.