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SubjectRE: [PATCH 02/10] perf tool: fix: Don't discard prev in backward mode
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> Em Tue, Oct 10, 2017 at 10:20:15AM -0700, kan.liang@intel.com escreveu:
> > From: Kan Liang <kan.liang@intel.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.

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@intel.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

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