Re: [PATCH V6 4/6] perf, x86: handle multiple records in PEBS buffer

[Peter Zijlstra]

On Fri, Apr 17, 2015 at 02:19:58PM +0000, Liang, Kan wrote:

> > But that brings us to patch 1 of this series, how is that correct in the face of
> > this? There is an arbitrary delay (A->B) added to the period.
> > And the Changelog of course never did bother to make that clear.
> 
> OK. I will update the changelog for patch 1 as below.
> ---
> When a fixed period is specified, this patch make perf use the PEBS
> auto reload mechanism. This makes normal profiling faster, because
> it avoids one costly MSR write in the PMI handler.

> However, the reset value will be loaded by hardware assist. There is 
> a little bit delay compared to previous non-auto-reload mechanism.
> The delay is arbitrary but very small.

What is very small? And doesn't that mean its significant at exactly the
point this patch series is aimed at, namely very short period.
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