On Fri, Oct 11, 2013 at 10:02:28AM +0530, Anshuman Khandual wrote:

On 10/11/2013 07:41 AM, Michael Ellerman wrote:

quoted

On Thu, Oct 10, 2013 at 02:20:22PM +0530, Anshuman Khandual wrote:

quoted

Even I think this is not right. Instruction sampling should have been
enabled before we enable PMU interrupts. Else there is a small window
of time where we could have the PMU enabled with events (which requires
sampling) without the sampling itself being enabled in MMCRA.

Yes I agree. That's a separate bug, which we'll need to test on all the book3s
platforms we have perf support for.

Okay, I guess any platform which supports sampling will definitely want to have
it enabled before we can set the events to count on PMU. Can you think of any
problem which can arise if we move it before the enabling the PMU back ? Else
we can fix this easily.

In theory it should be a trivial change. But hardware can behave in
strange ways, it's possible on some old chip we need to do it the
current way for some reason.

So although I don't think it will be a problem, it could be, so we
will need to test it thoroughly.

cheers