* Peter Zijlstra <pet...@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 <namhy...@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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