linux-kernel - Re: [PATCH v4 0/4] perf timechart io mode

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Date:	Wed, 25 Jun 2014 08:01:17 -0600
From:	David Ahern <dsahern@...il.com>
To:	Stanislav Fomichev <stfomichev@...dex-team.ru>
CC:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	acme@...nel.org, namhyung@...nel.org, artagnon@...il.com,
	rusty@...tcorp.com.au, bp@...e.de
Subject: Re: [PATCH v4 0/4] perf timechart io mode

On 6/25/14, 5:20 AM, Stanislav Fomichev wrote:
>>> maybe we dont need to fail in this case.. seems like it should
>>> not be hard to detect, wanr and recover? ;-)
> The easiest way is just to bail out and don't try to be smart, that's
> what I do now.
>
> Another approach would be to just convert all my consistency
> checks to warnings and skip invalid events (and hope it somehow works). I
> think it makes sense when for some reason we have perf.data which
> is not really consistent but we still want to get something out of it.

If the event type does not make sense how can you trust any other field 
-- like event size?

>
>> seems to me it should not be happening at all. It seems like the head caught
>> the tail and was not properly detected.
> So you mean it perf record's fault?
>

In my cases I am running perf-record. At the end of the session it walks 
the events and in too many cases I see the message:

  0x113f80 [0x8]: failed to process type: 68

So, yes I think something is happening during the record such as the 
writer passing the reader and corrupting the buffers.

David
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