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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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