Messages in this thread | | | Date | Wed, 20 Feb 2013 22:18:19 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf x86: Change SandyBridge and IvyBrige instructions event to be precise |
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On Wed, Feb 20, 2013 at 12:55:59PM -0800, Andi Kleen wrote: > Jiri Olsa <jolsa@redhat.com> 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. > > Actually it's possible, you just have to use it explicitely. > > This will break a lot of profiling setups that assume instructions > count on the fixed counter and use the 4/8 other counters. > Also it will give very bad results with perf stat, which > you don't want to run with pebs.
right, I haven't realized that..
> > Even worse with your change the fixed instruction counter is not > accessible anymore. So pretty much all the standard setups
still could be used explicitly via cpu/event=0xc0/
> that collect it in addition to other events and fill all > the counters would break. > > I don't think it should be done by default, but yes explicitely > it's quite useful. > > My Haswell patchkit (in the "extended version") exposes > the precise event as "instructions-p" through sysfs.
will check
thanks, jirka
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