Questions about when we take counter measurements, reset, etc

Chris Jones jones.chris.g at gmail.com
Mon Oct 13 16:40:00 PDT 2014


On Fri, Oct 3, 2014 at 5:18 PM, Kyle Huey <me at kylehuey.com> wrote:

> As an alternative, I starting looking into what it would take to move
> to just using absolute counter values everywhere, and then we could
> throw away caching/resetting/etc entirely.  Did cjones imagine when he
> filed #
> ​​
> 803 that we would switch to using
> ​​
> PERF_EVENT_IOC_PERIOD to
> reset the signalling mechanism?


I looked at using REFRESH in #599.  Unfortunately, I don't remember much
more beyond what I wrote in that issue.  I don't recall reading about
PERIOD.


> The man page[0] is a little
> concerning, stating that "Since ... Linux 3.14, the new period takes
> effect immediately. On older kernels, the new period did not take
> effect until after the next overflow".  The latter could be a problem,
> hence my earlier email about the kernel version.  I hacked up using
> IOC_PERIOD and it passes most but not all of the tests.  Upgrading my
> kernel to 3.14 to see if that fixes the rest was a bit too much for 4
> pm on a Friday.
>
>
​I don't have qualms about bumping up the minimum kernel version if it buys
us something significant.  We've already done that twice.

Cheers,
Chris​
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