Re: perf: regression with PERF_EVENT_IOC_REFRESH

[Vince Weaver]

On Sat, 28 May 2011, Peter Zijlstra wrote:

> On Fri, 2011-05-27 at 23:38 -0400, Vince Weaver wrote:
> > on that note (and while trying to document exactly what the ioctls do) it 
> > seems that a PERF_EVENT_IOC_REFRESH with an argument of anything higher 
> > than one does not work on kernels 2.6.36 and newer.  The behavior acts
> > as if 1 was passed, even if you pass in, say, 3.
> 
> Urgh, no that should definitely work. Thanks for the test-case, I'll
> work on that (probably not until Monday though, but who knows).
> 

after a painfully long bisection, it turns out that this problem was in
theory introduced by the following commit:

  d57e34fdd60be7ffd0b1d86bfa1a553df86b7172

  perf: Simplify the ring-buffer logic: make perf_buffer_alloc() do everything needed

I'll see if I can come up with a patch, but it's a bit non-obvious why
this commit is affecting the REFRESH value at all.

Vince
vweaver1@xxxxxxxxxxxx
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