linux-kernel - Re: [PATCH v7 2/6] perf record: Get the first sample time and last sample time

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Date:   Fri, 5 Jan 2018 09:53:41 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v7 2/6] perf record: Get the first sample time and last
 sample time

Em Fri, Jan 05, 2018 at 09:15:03AM +0800, Jin, Yao escreveu:
> 
> 
> On 1/5/2018 3:09 AM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Dec 08, 2017 at 09:13:42PM +0800, Jin Yao escreveu:
> > > In the default 'perf record' configuration, all samples are processed,
> > > to create the HEADER_BUILD_ID table. So it's very easy to get the
> > > first/last samples and save the time to perf file header via the
> > > function write_sample_time().
> > > 
> > > Later, at post processing time, perf report/script will fetch
> > > the time from perf file header.
> > 
> > So, at this point I was expecting that that record would be present on
> > the perf.data file:
> > 
> > [acme@...et perf]$ perf record --timestamp-boundary sleep 1
> > Cannot read kernel map
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.001 MB perf.data (7 samples) ]
> > [acme@...et perf]$ perf report -D | grep PERF_RECORD_SAMPLE | wc -l
> > 7
> > [acme@...et perf]$ perf report -D | grep PERF_RECORD_SAMPLE_TIME
> > [acme@...et perf]$
> > 
> > What am I doing wrong?
> > 
> > To clarify, this is with just the first two patches in this series
> > applied.
> > 
> > - Arnaldo
> 
> Hi Arnaldo,
> 
> The timestamp boundary information is saved in perf file header.

Right, my bad, I somehow thought it would be as PERF_RECORD_SAMPLE_TIME,
duh.

Will continue reviewing, sorry about that.

- Arnaldo
 
> So if we want to look at them, we need to add '--header' in perf report.
> 
> For example,
> 
> root@skl:/tmp# perf report -D --header | grep 'time of'
> # time of first sample : 248333.706656
> # time of last sample : 248357.215328
> 
> Thanks
> Jin Yao