linux-kernel - Re: [PATCH 6/7] perf kvm: move perf_kvm__mmap

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Date:	Mon, 23 Jun 2014 08:06:34 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Stanislav Fomichev <stfomichev@...dex-team.ru>
CC:	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	jolsa@...hat.com, xiaoguangrong@...ux.vnet.ibm.com,
	yangds.fnst@...fujitsu.com, adrian.hunter@...el.com,
	namhyung@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] perf kvm: move perf_kvm__mmap_read into session utils

On 6/20/14, 8:44 AM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Jun 20, 2014 at 02:49:48PM +0400, Stanislav Fomichev escreveu:
>> It will be reused by perf trace in the following commit.
>
> I know this is needed, but one of the goals when I started builtin-trace
> was not to use perf_session at all, as it initially was just about the
> live mode.
>
> record/replay came later and ended up needing it,

perf-kvm does not use the session code because I kept tripping over the 
out of order timestamp problem. By limiting the number of events read in 
a single pass I was able to smooth out the load and avoided hitting it 
as often. As I mentioned before the final piece was using the perf_clock 
timestamp at the start of the round to ensure I never hit it.

Stanislav: are you seeing out of order timestamp errors or just trying 
to reuse the live code from perf-kvm?

David
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