linux-kernel - Re: [PATCH] perf record: Add snapshot mode support for perf's regular events

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Message-ID: <20151125122038.GA17308@twins.programming.kicks-ass.net>
Date:	Wed, 25 Nov 2015 13:20:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Yunlong Song <yunlong.song@...wei.com>, paulus@...ba.org,
	mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
	namhyung@...nel.org, ast@...nel.org,
	masami.hiramatsu.pt@...achi.com, kan.liang@...el.com,
	adrian.hunter@...el.com, jolsa@...nel.org, dsahern@...il.com,
	bp@...en8.de, jean.pihet@...aro.org, rric@...nel.org,
	xiakaixu@...wei.com, hekuang@...wei.com
Subject: Re: [PATCH] perf record: Add snapshot mode support for perf's
 regular events

On Wed, Nov 25, 2015 at 05:44:00PM +0800, Wangnan (F) wrote:
> 
> 
> On 2015/11/25 17:27, Peter Zijlstra wrote:
> >On Tue, Nov 24, 2015 at 10:00:31PM +0800, Yunlong Song wrote:
> >>In our patch, we create and maintain a user space ring buffer to store
> >>perf's tracing info, instead of directly writing to perf.data file as
> >>before. In snapshot mode, only a SIGUSR2 signal can trigger perf to dump
> >>the tracing info currently stored in the user space ring buffer to
> >>perf.data file.
> >I would very much like to first fix the perf overwrite mode: see
> >lkml.kernel.org/r/20151023151205.GW11639@...ns.programming.kicks-ass.net
> 
> I think they can be done in parallel. We can first do something with
> tracking events and perf's output file, and wait for kernel level
> overwrite mode fixed, then decide whether to implement perf's own
> ringbuffer.

That seems backwards; why would you ever want to endlessly copy the
events if you're not going to use them?
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