linux-kernel - Re: [PATCH v2] perf doc: Document ring buffer mechanism

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Message-ID: <20230804091027.GC589820@leoy-yangtze.lan>
Date:   Fri, 4 Aug 2023 17:10:27 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jonathan Corbet <corbet@....net>, Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2] perf doc: Document ring buffer mechanism

On Thu, Aug 03, 2023 at 05:53:29PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Aug 04, 2023 at 12:56:36AM +0800, Leo Yan escreveu:
> > Hi Jon,
> > 
> > On Thu, Aug 03, 2023 at 08:34:50AM -0600, Jonathan Corbet wrote:
> > > Leo Yan <leo.yan@...aro.org> writes:
> > > 
> > > > In the Linux perf tool, the ring buffer serves not only as a medium for
> > > > transferring PMU event data but also as a vital mechanism for hardware
> > > > tracing using technologies like Intel PT and Arm CoreSight, etc.
> > > >
> > > > Consequently, the ring buffer mechanism plays a crucial role by ensuring
> > > > high throughput for data transfer between the kernel and user space
> > > > while avoiding excessive overhead caused by the ring buffer itself.
> > > >
> > > > This commit documents the ring buffer mechanism in detail.  It provides
> > > > an in-depth explanation of the implementation of both the generic ring
> > > > buffer and the AUX ring buffer.  Additionally, it covers how these ring
> > > > buffers support various tracing modes and explains the synchronization
> > > > with memory barriers.
> > > >
> > > > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > > > ---
> > > 
> > > So this seems like good material from a very brief scan.  I do have to
> > > ask, though: why is it not in RST, and why not put it into the
> > > user-space API book?
> > 
> > This documentation is Perf related topic, so my instinct is to place
> > it into the folder tools/perf/Documentation/.
> > 
> > Strictly to say, the doc doesn't give formal introduction for the
> > user-space APIs.  Given perf ring buffer is a mechanism for exchanging
> > data between the kernel and user space, I am open for placing it in the
> > folder Documentation/userspace-api/.
> > 
> > I would like get opinions from the perf maintainers if possible, if we
> > have agreenment I am glad to convert it to RST format.
> 
> Yeah, I agree with Jon.

Okay, I will spin a new patch based on this discussion.

Thanks for confirmation.

Leo