linux-kernel - Re: [PATCH 1/3] perf tools: Fix period/freq terms setup

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Date:   Mon, 5 Feb 2018 18:13:40 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/3] perf tools: Fix period/freq terms setup

Em Mon, Feb 05, 2018 at 12:58:16PM -0800, Stephane Eranian escreveu:
> On Mon, Feb 5, 2018 at 7:17 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> > On Fri, Feb 02, 2018 at 01:04:34PM -0800, Stephane Eranian wrote:
> >> On Fri, Feb 2, 2018 at 12:40 PM, Arnaldo Carvalho de Melo
> >> <acme@...nel.org> wrote:
> >> > Em Fri, Feb 02, 2018 at 05:28:49PM -0300, Arnaldo Carvalho de Melo escreveu:
> >> >> Em Fri, Feb 02, 2018 at 10:45:46AM -0800, Stephane Eranian escreveu:
> >> >> > Otherwise, I tested what you have written so far and it works.
> >> >
> >> >> So I take that as a Tested-by: Stephane and will apply the patches, Jiri
> >> >> can continue working on these other aspects, right?
> >> >
> >> > I also added this for the casual reader to get up to speed more quickly,
> >> > please check that it makes sense.
> >> >
> >> >     Committer note:
> >> >
> >> >     When we use -c or a period=N term in the event definition, then we don't
> >> >     need to ask the kernel, via perf_event_attr.sample_type |=
> >> >     PERF_SAMPLE_PERIOD, to put the event period in each sample, as we know
> >> >     it already, it is in perf_event_attr.sample_period.
> >> >
> >> Not quite. It depends on how each event is setup. I can mix & match period
> >> and frequency. The PERF_SAMPLE_PERIOD can be dropped only if all the
> >> events use a fixed period either via period=N or -c.

> > I think you can have both period and freq based event in one session
> > if that's your concern..? what would be the problem?

> My understanding was that perf only support configs where all events
> have the same attr.sample_type. With frequency mode, you'd want the period
> recorded in some cases.

[root@...et ~]# perf record -e cycles/period=2/,instructions/freq=100/
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 1.895 MB perf.data (122 samples) ]

[root@...et ~]# perf report
[root@...et ~]# perf evlist -v
cycles/period=2/: size: 112, { sample_period, sample_freq }: 2, sample_type: IP|TID|TIME|CPU|IDENTIFIER, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1
instructions/freq=100/: size: 112, config: 0x1, { sample_period, sample_freq }: 100, sample_type: IP|TID|TIME|CPU|PERIOD|IDENTIFIER, read_format: ID, disabled: 1, inherit: 1, freq: 1, sample_id_all: 1, exclude_guest: 1
[root@...et ~]# 

commit ff3d527cebc1fa3707c617bfe9e74f53fcfb0955
Author: Adrian Hunter <adrian.hunter@...el.com>
Date:   Tue Aug 27 11:23:07 2013 +0300

    perf: make events stream always parsable
    
    The event stream is not always parsable because the format of a sample
    is dependent on the sample_type of the selected event.  When there is
    more than one selected event and the sample_types are not the same then
    parsing becomes problematic.  A sample can be matched to its selected
    event using the ID that is allocated when the event is opened.
    Unfortunately, to get the ID from the sample means first parsing it.
    
    This patch adds a new sample format bit PERF_SAMPLE_IDENTIFER that puts
    the ID at a fixed position so that the ID can be retrieved without
    parsing the sample.  For sample events, that is the first position
    immediately after the header.  For non-sample events, that is the last
    position.
    
    In this respect parsing samples requires that the sample_type and ID
    values are recorded.  For example, perf tools records struct
    perf_event_attr and the IDs within the perf.data file.  Those must be
    read first before it is possible to parse samples found later in the
    perf.data file.
    
    Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
    Tested-by: Stephane Eranian <eranian@...gle.com>
    Acked-by: Peter Zijlstra <peterz@...radead.org>