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Date:   Tue, 14 Sep 2021 11:51:36 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Mike Leach <mike.leach@linaro.org>,
        Michael Petlan <mpetlan@redhat.com>,
        "Frank Ch. Eigler" <fche@redhat.com>,
        Song Liu <songliubraving@fb.com>, x86@kernel.org,
        Daniel =?iso-8859-1?Q?D=EDaz?= <daniel.diaz@linaro.org>,
        Andrii Nakryiko <andriin@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        coresight@lists.linaro.org
Subject: Re: [PATCH v5 4/9] perf/x86: Add compiler barrier after updating BTS
Message-ID: <YUBwqGuQskkw328z@hirez.programming.kicks-ass.net>
References: <20210809111407.596077-1-leo.yan@linaro.org>
 <20210809111407.596077-5-leo.yan@linaro.org>
 <20210829105657.GC14461@leoy-ThinkPad-X240s>
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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?

> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> >  arch/x86/events/intel/bts.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
> > index 6320d2cfd9d3..974e917e65b2 100644
> > --- a/arch/x86/events/intel/bts.c
> > +++ b/arch/x86/events/intel/bts.c
> > @@ -209,6 +209,12 @@ static void bts_update(struct bts_ctx *bts)
> >  	} else {
> >  		local_set(&buf->data_size, head);
> >  	}
> > +
> > +	/*
> > +	 * Since BTS is coherent, just add compiler barrier to ensure
> > +	 * BTS updating is ordered against bts::handle::event.
> > +	 */
> > +	barrier();
> >  }
> >  
> >  static int
> > -- 
> > 2.25.1
> >