linux-kernel - Re: [PATCH RFC] perf kvm stat live: cache mmap()ed events

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Date:	Sun, 14 Sep 2014 09:39:37 -0600
From:	David Ahern <dsahern@...il.com>
To:	Alexander Yarygin <yarygin@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH RFC] perf kvm stat live: cache mmap()ed events

On 9/12/14, 10:27 AM, Alexander Yarygin wrote:
> During mmap() process 'perf kvm stat live' gets a pointer to events and
> passes them to the session queue. Events are stored in shared memory and
> eventually they will be overwritten by the kernel. The problem is, that
> when events come too fast, old events can be overwritten before they
> have been processed that can lead to perf crash.
>
> To prevent that happening, we can copy upcoming events and pass a copy
> to the session queue. There is a safe place to copy event: before
> perf_evlist__mmap_consume() is executed. There are 3 places to free it:
> when event is processed, when it's lost and on exit, if it's turned out
> unprocessed.

Did you see what I proposed a year ago:
https://lkml.org/lkml/2013/9/6/388

The intent is to keep the copy generic and not local a command since 
conceptually other live commands need the same.

David
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