Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

From	David Ahern <dsahern@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)
Date	2015-12-14 15:50 +0100
Message-ID	<qFCBQ-7sa-17@gated-at.bofh.it> (permalink)
References	(1 earlier) <qE4sy-3sW-9@gated-at.bofh.it> <qE55f-3L0-3@gated-at.bofh.it> <qEr5L-1BY-11@gated-at.bofh.it> <qExuy-69x-11@gated-at.bofh.it> <qFxCa-4ar-15@gated-at.bofh.it>
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On 12/14/15 2:26 AM, Peter Zijlstra 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.

I've gone from the 1024-cpu sparc systems earlier this year down to 
small PPC and Rangeley-based switches. For both ends of the scale (and 
in between) I constantly struggle with the options to manage memory, cpu 
and disk consumption.

There definitely needs to be options (e.g., multi-threaded on/off). For 
the threading options I get the appeal for 1-thread per cpu but other 
options make sense as well -- 1 thread per core, 1 per NUMA node. perf 
has the CPU topology so should not be too difficult.

If you have 1-thread per cpu that means you are pinning the threads to 
the cpu? That brings in additional permissions problems.
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Thread

Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 10:30 +0100
  Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Ingo Molnar <mingo@kernel.org> - 2015-12-14 10:40 +0100
    Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) David Ahern <dsahern@gmail.com> - 2015-12-14 16:00 +0100
      Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Arnaldo Carvalho de Melo <acme@kernel.org> - 2015-12-14 17:30 +0100
        Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 17:50 +0100
          Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Arnaldo Carvalho de Melo <acme@kernel.org> - 2015-12-14 19:00 +0100
    Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Namhyung Kim <namhyung@kernel.org> - 2015-12-14 17:40 +0100
      Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 18:00 +0100
        Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Namhyung Kim <namhyung@kernel.org> - 2015-12-14 18:20 +0100
  Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) David Ahern <dsahern@gmail.com> - 2015-12-14 15:50 +0100
    Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Namhyung Kim <namhyung@kernel.org> - 2015-12-14 18:10 +0100
      Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Arnaldo Carvalho de Melo <acme@kernel.org> - 2015-12-14 19:00 +0100
  Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Namhyung Kim <namhyung@kernel.org> - 2015-12-14 17:30 +0100
    Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1) Peter Zijlstra <peterz@infradead.org> - 2015-12-14 17:50 +0100

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