Questions about when we take counter measurements, reset, etc

Robert O'Callahan robert at
Fri Oct 3 19:26:46 PDT 2014

On Fri, Oct 3, 2014 at 8:18 PM, Kyle Huey <me at> wrote:

> I've been looking at reviving
>  The way we
> cache performance counters in Task and reset those, as well as reset
> the actual counters we read from is posing some problems.  This
> caching/resetting/etc happens at points that don't matter for retired
> conditional branches but do matter for instructions retired.  I don't
> think I understand things enough to try to rearrange them though.
> What's the logic/reasoning behind the points at which we take
> measurements, the points at which we reset, etc?

The current approach is roughly that we measure and reset the counter every
time we stop and then restart the task. This isn't very clear though; we
should make it clearer by removing ticks_read() and always measuring and
resetting the tick counter in wait().

BTW why do you want to do this work to switch to the instructions-retired
counter? AFAIK there is no guarantee it's viable.

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