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    SubjectRe: [rfc 1/3] perf, x86: P4 PMU - describe config format
    On Fri, Nov 26, 2010 at 05:22:51PM +0100, Stephane Eranian wrote:
    > On Fri, Nov 26, 2010 at 4:27 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
    > > On Fri, Nov 26, 2010 at 02:54:39PM +0100, Stephane Eranian wrote:
    > > ...
    > >> >
    > >> > No, single thread mode means _any_ single thread is running,
    > >> > Stephane I'll describe some more a bit later (as only reach home),
    > >> > ok?
    > >>
    > >> From the manual:
    > >>
    > >> 00 — None. Count only when neither logical processor is active.
    > >> 01 — Single. Count only when one logical processor is active (either 0 or 1).
    > >> 10 — Both. Count only when both logical processors are active.
    > >> 11 — Any. Count when either logical processor is active.
    > >>
    > >> In per-thread mode, you won't hit 00. I suspect you want to
    > >> disallow 01, 10 (or CAP_SYS_ADMIN). Otherwise, you want
    > >> to force 11, i.e., can't figure out what's going on in the other
    > >> HT thread.
    > >>
    > >
    > >  No ;) The key moment here that this flags are related to _activity_ of
    > > logical thread and I guess they were introduced just to allow measuring
    > > if user-space application does win from using HT or not (since for
    > > some loads the HT simply drops the perfomance).
    > >
    >
    > I think what they call 'logical CPU' is what the kernel calls CPU.

    yes

    > So I think bits 16-17 are used if you want to measure on CPU0 only
    > when CPU1 (assume both share the same physical core) is active
    > or inactive or don't care. You're right that I believe this mode was
    > introduced to measure the level of concurrency between HT
    > thread (logical CPUs).

    but "single thread mode" measures the event if *any* thread
    is active at a time, if we would assume that your assumption
    is right -- there would be no need for T1_OS/T1_USR.

    So I must admit I'm confused, the Oprofile do things simplier --
    it just sets "thread any" ;)

    >
    > In architectural perfmon the .any modifier is slightly different.
    > It indicates whether you want to measure only yourself or both
    > threads (regardless of the state of the other HT thread). In other
    > words, it is not because .any=1 that the event counts ONLY when
    > both threads (logical CPUs) are active.
    >
    ...

    Stephane, could you do a test? We need a pinned event which would be
    running on say cpu0 only and if you set P4_CCCR_THREAD_SINGLE in CCCR
    and event would be still incrementing -- this mean my theory is correct
    and this "thread" field means "when" to count, if not -- you're right
    and "thread" field means "where" instead.

    Cyrill
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