Re: [PATCH 0/2] x86/intel_rdt and perf/x86: Fix lack of coordination with perf

Peter Zijlstra
2018-08-08T16:47:36Z

On Wed, Aug 08, 2018 at 03:55:54PM +0000, Luck, Tony wrote:
> > So _why_ doesn't this work? As said by Tony, that first call should
> > prime the caches, so the second and third calls should not generate any
> > misses.
>
> How much code/data is involved? If there is a lot, then you may be unlucky
> with cache coloring and the later parts of the "prime the caches" code path
> may evict some lines loaded in the early parts.

Well, Reinette used perf_event_read_local() which is unfortunately quite
a bit. But the inline I proposed is a single load and depending on
rdpmcl() or native_read_pmc() a call to or just a single inline asm
rdpmc instruction.

That should certainly work I think.