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

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Date:	Tue, 15 Dec 2015 01:25:35 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Ahern <dsahern@...il.com>, Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

Hi Peter,

On Mon, Dec 14, 2015 at 10:26:13AM +0100, 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@...il.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.

Yes, but perf-record and perf-top is different.  The perf-record
merely saves the data into file while perf-top read events and process
them at the same time without file.  So we should choose different
default IMHO.

I want to focus on perf-top for now, once it's in a good shape, I'll
work on perf record/report too.


> 
> And in an unrelated note, I absolutely detest --buildid being the
> default, it makes perf-record blow chunks.

Maybe we can add a config option?

Thanks,
Namhyung
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