Messages in this thread | | | Date | Mon, 14 Dec 2015 10:38:41 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> On Fri, Dec 11, 2015 at 08:01:31AM -0700, David Ahern wrote: > > On 12/11/15 1:11 AM, Ingo Molnar wrote: > > > > > >* Namhyung Kim <namhyung@gmail.com> wrote: > > > > > >>IIRC David said that thread per cpu seems too much especially on a large system > > >>(like ~1024 cpu). [...] > > > > > >Too much in what fashion? For recording I think it's the fastest, most natural > > >model - anything else will create cache line bounces. > > > > The intrusiveness of perf on the system under observation. I understand > > there are a lot of factors that go into it. > > So I can see some of that, if every cpu has its own thread then every > cpu will occasionally schedule that thread. Whereas if there were less, > you'd not have that. > > Still, I think it makes sense to implement it, we need the multi-file > option anyway. Once we have that, we can also implement a per-node > option, which should be a fairly simple hybrid of the two approaches. > > The thing is, perf-record is really struggling on big machines. > > And in an unrelated note, I absolutely detest --buildid being the > default, it makes perf-record blow chunks.
So I'd absolutely _love_ to split up the singular perf.data into a hierarchy of files in a .perf directory, with a structure like this (4-core system):
.perf/cmdline .perf/features .perf/evlist .perf/ring_buffers/cpu0/raw.trace .perf/ring_buffers/cpu1/raw.trace .perf/ring_buffers/cpu2/raw.trace .perf/ring_buffers/cpu3/raw.trace ...
I.e. the current single file format of perf.data would be split up into individual files. Each CPU would get its own trace file output - any sorting and ordering would be done afterwards. 'perf record' itself would never by default have to do any of that, it's a pure recording session.
'perf archive' would still create a single file to make transport between machines easy.
perf.data.old would be replaced by a .perf.old directory or so.
Debugging would be easier too I think, as there's no complex perf data format anymore, it's all in individual (typically text, or binary dump) files in the .perf directory.
This would solve all the scalability problems - and would make the format more extensible and generally more accessible as well.
What do you think?
Thanks,
Ingo
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