On Wed, Feb 20, 2013 at 10:01:20PM +0100, Stephane Eranian wrote: > On Wed, Feb 20, 2013 at 9:55 PM, Andi Kleen <[email protected]> wrote: > > Jiri Olsa <[email protected]> writes: > > > >> Changing the default 'instructions' HW event for SandyBridge and > >> IvyBrige to use the available precise 'instructions' event. > >> > >> The precise event is defined in Intel SDM as: > >> > >> INST_RETIRED.ALL - Precise instruction retired event with HW to > >> reduce effect of PEBS shadow in IP distribution > >> > >> for both SandyBridge and IvyBrige micro-archs. It allows to use > >> precise modifier on 'instructions' event on SandyBridge and > >> IvyBrige micro-archs which is not possible now. > > > There is also the problem that on SNB, PREC_DIST must be > taken ALONE to be correct. By that, I mean no other counter > must be active. So I don't think it is a good idea. > > Also PREC_DIST is marked as constrained to counter 2 only. > That in effect, as Andi pointed out, will make the fixed counter > for instruction_retired, unused because you've set a umask now. > > I don't think it buys you much. People read too much into what > PEBS gives you. I can show you examples where PEBS > is worse than no PEBS.
well, we sort of advertise we have precise event via precise modifier and it confused me I was not able to use it on IvyBridge.. maybe we could export precise alias in sysfs as well which we could check & use any time there's 'p' modifier specified not pretty.. meeds more thinking ;-) thanks, jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
