Messages in this thread | | | Date | Fri, 26 Nov 2010 20:16:42 +0300 | From | Cyrill Gorcunov <> | Subject | Re: [rfc 1/3] perf, x86: P4 PMU - describe config format |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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