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From: "firstname.lastname@example.org" <email@example.com>
To: Rob Herring <firstname.lastname@example.org>
Cc: "email@example.com" <firstname.lastname@example.org>,
Subject: Re: [PATCH 1/3] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing
Date: Tue, 24 Aug 2021 10:11:28 +0000 [thread overview]
Message-ID: <OSBPR01MB4600288E176A169C07BF543EF7C59@OSBPR01MB4600.jpnprd01.prod.outlook.com> (raw)
> On Fri, Aug 20, 2021 at 06:39:06PM +0900, Shunsuke Nakamura wrote:
> > perf_evsel__read() scales counters obtained by RDPMC during multiplexing, but
> > does not scale counters obtained by read() system call.
> > Add processing to perf_evsel__read() to scale the counters obtained during the
> > read() system call when multiplexing.
> Which one is right though? Changing what read() returns could break
> users, right? Or are you implying that the RDPMC path is correct and
> read() was not. More likely the former case since I wrote the latter.
perf_evsel__read() returns both the count obtained by RDPMC and the count obtained
by the read() system call when multiplexed with RDPMC enabled.
That is, there is a mix of scaled and unscaled values.
As Rob says, when this patch is applied, rescaling the count obtained from
perf_evsel__read() during multiplexing will break the count.
I think the easiest solution is to change the value you get from RDPMC to not scale
and let the user scale it, but I thought it would be a little inconvenient.
next prev parent reply other threads:[~2021-08-24 10:18 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-20 9:39 [PATCH 0/3] libperf: Add support for scaling counters obtained from the read() system call during multiplexing Shunsuke Nakamura
2021-08-20 9:39 ` [PATCH 1/3] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing Shunsuke Nakamura
2021-08-23 20:12 ` Rob Herring
2021-08-24 10:11 ` nakamura.shun [this message]
2021-08-31 8:58 ` nakamura.shun
2021-08-31 12:26 ` Rob Herring
2021-09-07 23:59 ` Ian Rogers
2021-09-17 8:04 ` nakamura.shun
2021-08-20 9:39 ` [PATCH 2/3] libperf tests: Fix verbose printing Shunsuke Nakamura
2021-08-23 20:26 ` Rob Herring
2021-08-24 18:06 ` Arnaldo Carvalho de Melo
2021-08-20 9:39 ` [PATCH 3/3] libperf tests: Add test_stat_multiplexing test Shunsuke Nakamura
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