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    SubjectRe: [PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi
    On Mon, Jun 19, 2017 at 04:37:41PM +0300, Alexey Budankov wrote:
    > On 19.06.2017 16:26, Mark Rutland wrote:
    > >On Mon, Jun 19, 2017 at 04:08:32PM +0300, Alexey Budankov wrote:
    > >>On 16.06.2017 1:10, Alexey Budankov wrote:
    > >>>On 15.06.2017 22:56, Mark Rutland wrote:
    > >>>>On Thu, Jun 15, 2017 at 08:41:42PM +0300, Alexey Budankov wrote:
    > >>>>>This series of patches continues v2 and addresses captured comments.
    > >
    > >>>>>Specifically this patch replaces pinned_groups and flexible_groups
    > >>>>>lists of perf_event_context by red-black cpu indexed trees avoiding
    > >>>>>data structures duplication and introducing possibility to iterate
    > >>>>>event groups for a specific CPU only.
    > >
    > >>>>Have you thrown Vince's perf fuzzer at this?
    > >>>>
    > >>>>If you haven't, please do. It can be found in the fuzzer directory of:
    > >>>>
    > >>>>https://github.com/deater/perf_event_tests
    > >>>
    > >>>Accepted.
    > >>
    > >>I run the test suite and it revealed no additional regressions in
    > >>comparison to what I have on the clean kernel.
    > >>
    > >>However the fuzzer constantly reports some strange stacks that are
    > >>not seen on the clean kernel and I have no idea how that might be
    > >>caused by the patches.
    > >
    > >Ok; that was the kind of thing I was concerned about.
    > >
    > >What you say "strange stacks", what do you mean exactly?
    > >
    > >I take it the kernel spewing backtraces in dmesg?
    > >
    > >Can you dump those?
    >
    > Here it is:
    >
    > list_del corruption. prev->next should be ffff88c2c4654010, but was
    > ffff88c31eb0c020
    > [ 607.632813] ------------[ cut here ]------------
    > [ 607.632816] kernel BUG at lib/list_debug.c:53!

    > [ 607.635531] Call Trace:
    > [ 607.635583] list_del_event+0x1d7/0x210

    Given this patch changes how list_{del,add}_event() works, it's possible
    that this is a new bug.

    I was going to try to test this on arm64, but I couldn't get the patch
    to apply. I had a go with v4.12-rc5, tip/perf/core, and tip/perf/urgent.

    Which branch should I be using as the base?

    Thanks,
    Mark

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