Messages in this thread | | | Date | Mon, 14 Dec 2015 10:26:13 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) |
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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.
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