linux-kernel - Re: [PATCH 02/10] perf tool: fix: Don't discard prev in backward mode

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Message-ID: <20171013131312.GL3503@kernel.org>
Date:   Fri, 13 Oct 2017 10:13:12 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "wangnan0@...wei.com" <wangnan0@...wei.com>,
        "hekuang@...wei.com" <hekuang@...wei.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH 02/10] perf tool: fix: Don't discard prev in backward mode

Em Fri, Oct 13, 2017 at 12:55:34PM +0000, Liang, Kan escreveu:
> > Em Tue, Oct 10, 2017 at 10:20:15AM -0700, kan.liang@...el.com escreveu:
> > > From: Kan Liang <kan.liang@...el.com>
> > >
> > > Perf record can switch output. The new output should only store the
> > > data after switching. However, in overwrite backward mode, the new
> > > output still have the data from old output.
> > >
> > > At the end of mmap_read, the position of processed ring buffer is
> > > saved in md->prev. Next mmap_read should be end in md->prev.
> > > However, the md->prev is discarded. So next mmap_read has to process
> > > whole valid ring buffer, which definitely include the old processed
> > > data.
> > >
> > > Set the prev as the end of the range in backward mode.
> > 
> > Do you think this should go together with the rest of this patchkit?
> > Probably it should be processed ASAP, i.e. perf/urgent, no?
> >
> 
> Hi Arnaldo,
> 
> After some discussion, Wang Nan proposed a new patch to fix this issue.
> https://lkml.org/lkml/2017/10/12/441
> I did some tests. It fixed the issue.

Ok, I'll look at it and stick a "Tested-by: Kan", ok?

- Arnaldo
 
> Could you please take a look?
> If it's OK for you, I think it could be merged separately.
> 
> Thanks,
> Kan
>  
> > - Arnaldo
> > 
> > > Signed-off-by: Kan Liang <kan.liang@...el.com>
> > > ---
> > >  tools/perf/util/evlist.c | 14 +++++++++++++-
> > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index
> > > 33b8837..7d23cf5 100644
> > > --- a/tools/perf/util/evlist.c
> > > +++ b/tools/perf/util/evlist.c
> > > @@ -742,13 +742,25 @@ static int
> > >  rb_find_range(void *data, int mask, u64 head, u64 old,
> > >  	      u64 *start, u64 *end, bool backward)  {
> > > +	int ret;
> > > +
> > >  	if (!backward) {
> > >  		*start = old;
> > >  		*end = head;
> > >  		return 0;
> > >  	}
> > >
> > > -	return backward_rb_find_range(data, mask, head, start, end);
> > > +	ret = backward_rb_find_range(data, mask, head, start, end);
> > > +
> > > +	/*
> > > +	 * The start and end from backward_rb_find_range is the range for
> > all
> > > +	 * valid data in ring buffer.
> > > +	 * However, part of the data is processed previously.
> > > +	 * Reset the end to drop the processed data
> > > +	 */
> > > +	*end = old;
> > > +
> > > +	return ret;
> > >  }
> > >
> > >  /*
> > > --
> > > 2.5.5