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    SubjectRe: [RFCv2 00/48] perf tools: Add threads to record command

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > On Fri, Sep 14, 2018 at 01:47:25PM +0200, Jiri Olsa wrote:
    > > On Fri, Sep 14, 2018 at 01:15:28PM +0200, Peter Zijlstra wrote:
    > > > On Fri, Sep 14, 2018 at 11:40:22AM +0200, Ingo Molnar wrote:
    > > > > In fact keeping the files separate has scalability advantages for 'perf report' and similar
    > > > > parsing tools: they could read all the streams in a per-CPU fashion already, from the very
    > > > > beginning.
    > > >
    > > > Also writing to different files from different CPUs is good for record,
    > > > less contention on the inode state (which include pagecache).
    > >
    > > maybe I should explain a little bit more on this
    > >
    > > we write to different (per-cpu) files during the record,
    > > and at the end of the session, we take them and store
    > > them inside perf.data
    >
    > How long does it take to combine that? If we generated a lot of data,
    > that could take a fair amount of time, no?
    >
    > I feel that record should not mysteriously 'hang' when it is done. It
    > used to do that at some point because of that stupid .debug crap, but
    > acme fixed that I think.

    Agreed - plus at the report stage it would be advantageous to be able to *read* per-cpu files
    as well.

    If we do things smartly them report will create similar NUMA affinity as the record session
    used.

    Thanks,

    Ingo

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