linux-kernel - Re: [PATCH v5 4/9] perf/x86: Add compiler barrier after updating BTS

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Message-ID: <YUCLzrMyx2yhBE7E@hirez.programming.kicks-ass.net>
Date:   Tue, 14 Sep 2021 13:47:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Michael Petlan <mpetlan@...hat.com>,
        "Frank Ch. Eigler" <fche@...hat.com>,
        Song Liu <songliubraving@...com>, x86@...nel.org,
        Daniel Díaz <daniel.diaz@...aro.org>,
        Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org
Subject: Re: [PATCH v5 4/9] perf/x86: Add compiler barrier after updating BTS

On Tue, Sep 14, 2021 at 06:05:17PM +0800, Leo Yan wrote:
> Hi Peter,
> 
> On Tue, Sep 14, 2021 at 11:51:36AM +0200, Peter Zijlstra wrote:
> > On Sun, Aug 29, 2021 at 06:56:57PM +0800, Leo Yan wrote:
> > > Hi Peter, or any x86 maintainer,
> > > 
> > > On Mon, Aug 09, 2021 at 07:14:02PM +0800, Leo Yan wrote:
> > > > Since BTS is coherent, simply add a compiler barrier to separate the BTS
> > > > update and aux_head store.
> > > 
> > > Could you reivew this patch and check if BTS needs the comipler
> > > barrier in this case?  Thanks.
> > 
> > Yes, a compiler barrier is sufficient.
> > 
> > You want me to pick it up?
> 
> Maybe other maintainers are more suitable than me to answer this :)
> 
> Yeah, I think it's great if you could pick it.

OK, done.