On Mon, Apr 15, 2013 at 6:13 PM, Vince Weaver <[email protected]> wrote: > > It turns out that perf_event for intel seems to use the INST_RETIRED.ALL > event interchangably with the "Fixed Counter 0" event. > Yes, it does.
> It turns out they are not equivelent. The Fixed Counter 0 event turns out > to be deterministic, while INST_RETIRED.ALL has a bug where it counts > extra events due to hardware interrupts. > Never heard of that problem. I know there was another problem due to leaking during priv level transitions. It would be take a few instr or cycles to realize you were not in user level any more when doing event:u. Interrupt should impact fixed and generic counters the same way. > Having a user-accessible deterministic instructions event would be really > useful. So is there a way we can specify we want an event to run on Fixed > Counter 0? I think there is code already that does this for Fixed Counter > 2 for similar reasons. > No. Fixed counter 2 (ref-cycles) is a different reason. It's because it measures an event that does not exist on generic counters: unhalted_reference_cycles. > For an example of this happening in real life, take the > ./retired_instr.all.x86_64 from my deterministic benchmark that > I'll be presenting at the ISPASS conference next week. > (can be found here git://github.com/deater/deterministic.git ) > > If you run this benchmark with the same event listed 5 times on an Ivy > Bridge machine you get these results, notice the last one is the "proper" > deterministic result and thus the one that ran on Fixed Counter 0. > Are you sure that the 5th event stayed in fixed counter 0 all along? > $ perf stat -e > instructions:u,instructions:u,instructions:u,instructions:u,instructions:u > ./retired_instr.all.x86_64 > ... > Performance counter stats for './retired_instr.all.x86_64': > > 227,010,687 instructions:u # 0.00 insns per cycle > 227,010,687 instructions:u # 0.00 insns per cycle > 227,010,687 instructions:u # 0.00 insns per cycle > 227,010,687 instructions:u # 0.00 insns per cycle > 227,000,723 instructions:u # 0.00 insns per cycle > > 1.902648316 seconds time elapsed > > Thanks, > > Vince Weaver > [email protected] > http://www.eece.maine.edu/~vweaver/ -- 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/
