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    SubjectRe: [PATCH 4/4] perf script: Add script to collect and display IBS samples

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Fri, 2011-12-23 at 14:53 +0100, Ingo Molnar wrote:
    > > * Robert Richter <robert.richter@amd.com> wrote:
    > >
    > > > > Also, could you quote example output of "perf script report
    > > > > ibs"?
    > > >
    > > > IBS_FETCH sample on cpu6 IBS0: 0x00170003186a186a IBS1: 0x0000000000444780 IBS2:0x000000041af26780
    > > > IBS_FETCH sample on cpu6 IBS0: 0x00170003186a186a IBS1: 0x00007f5efb44e3b2 IBS2:0x000000042fcff3b2
    > > > IBS_FETCH sample on cpu6 IBS0: 0x01370003186a186a IBS1: 0xffffffff81065273 IBS2:0x0000000001065273
    > > > IBS_FETCH sample on cpu6 IBS0: 0x01370003186a186a IBS1: 0xffffffff811a6320 IBS2:0x00000000011a6320
    > > > IBS_FETCH sample on cpu6 IBS0: 0x01370003186a186a IBS1: 0xffffffff81065255 IBS2:0x0000000001065255
    > > > IBS_FETCH sample on cpu7 IBS0: 0x00170004186a186a IBS1: 0x00007fbf0c687ca0 IBS2:0x000000041d345ca0
    > > > IBS_FETCH sample on cpu7 IBS0: 0x00170003186a186a IBS1: 0x000000000043bb80 IBS2:0x000000041c351b80
    > > > IBS_FETCH sample on cpu7 IBS0: 0x01370003186a186a IBS1: 0xffffffff813d5790 IBS2:0x00000000013d5790
    > > > IBS_FETCH sample on cpu7 IBS0: 0x00030001186a186a IBS1: 0xffffffff8102bd00 IBS2:0x00000000013d5d00
    > >
    > > That does not look very usable to users. So why should we merge
    > > this new ABI in its incomplete form with no complete usecase?
    > > Being usable is clearly not outside the scope of a new feature
    > > ...
    > >
    > > Integrating it into perf report should not be *that* hard,
    > > you've done most of the hard work already. But without that
    > > step we just don't know how complete and usable the whole
    > > thing is.
    >
    > perf annotate like output might make more sense for IBS, maybe
    > not decode all the information that's in there, but at least a
    > number of the most useful measurements for each type and
    > present multiple columns in front of the instructions.
    >
    > Ingo, the trouble with IBS is that it doesn't measure
    > something, its a measure everything together like thing, so
    > what particular part of this massive bulk data do you use to
    > create your histograms?

    My point is that a useful angle to it has to be presented for it
    to be useful for upstream.

    The bit that looks useful about IBS is skid-free sampling. So as
    long as the 'bulk data' contains enough information to do a
    'perf record -e instructions:p' work-alike thing it would be
    useful, right?

    Sadly precise cycles sampling is not possible via IBS, right?

    Thanks,

    Ingo

    [*] Sidenote: i suspect the RIP+1 sampling artifact cannot be
    gotten rid of on AMD CPUs, right?



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