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Date: Wed, 6 Jun 2012 07:16:44 -0700 From: Andi Kleen <ak@...ux.intel.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org, eranian@...gle.com Subject: Re: [PATCH 5/5] perf, x86: Prefer RDPMC over RDMSR for reading counters On Wed, Jun 06, 2012 at 12:46:19PM +0200, Peter Zijlstra wrote: > On Tue, 2012-06-05 at 17:56 -0700, Andi Kleen wrote: > > From: Andi Kleen <ak@...ux.intel.com> > > > > RDPMC is much faster than RDMSR for reading performance counters, > > since it's not serializing. Use it if possible in the perf handler. > > > > Only tested on Sandy Bridge, so I only enabled it there so far. > > That's just stupid.. I took Vince's patch from a while back. What do you mean? It's significantly faster to read the counters this way, because it avoids serialization and other overhead. Vince's patch only enabled it for user space I believe, This is for lowering the kernel PMI handler overhead. -Andi -- ak@...ux.intel.com -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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