linux-kernel - Re: [PATCH v1 3/7] perf cs-etm: Calculate per CPU metadata array size

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Message-ID: <20210116005046.GB5418@leoy-ThinkPad-X240s>
Date:   Sat, 16 Jan 2021 08:50:46 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Mike Leach <mike.leach@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Daniel Kiss <Daniel.Kiss@....com>,
        Denis Nikitin <denik@...omium.org>,
        Coresight ML <coresight@...ts.linaro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/7] perf cs-etm: Calculate per CPU metadata array size

Hi Mathieu,

On Fri, Jan 15, 2021 at 03:46:58PM -0700, Mathieu Poirier wrote:
> On Mon, Jan 11, 2021 at 12:09:12PM +0000, Mike Leach wrote:
> > Hi Leo,
> > 
> > I think there is an issue here in that your modification assumes that
> > all cpus in the system are of the same ETM type. The original routine
> > allowed for differing ETM types, thus differing cpu ETM field lengths
> > between ETMv4 / ETMv3, the field size was used after the relevant
> > magic number for the cpu ETM was read.
> > 
> > You have replaced two different sizes - with a single calculated size.
> 
> I usually go through an entire patchset before looking at the comments people
> have made.  In this case Mike and I are coming to the exact same conclusion.

Agreed, now this work depends on Mike's patch for extending metadata
version; otherwise if without Mike's patch, it will cause compability
issue.

> I will look at Mike's patch on Monday.

Cool!

Thanks for review,
Leo