Messages in this thread | | | Date | Tue, 19 Apr 2011 20:21:48 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH 3/4] perf, x86: Use ALTERNATIVE() to check for X86_FEATURE_PERFCTR_CORE |
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On Tue, Apr 19, 2011 at 12:39:27PM +0200, Robert Richter wrote: > On 18.04.11 16:00:57, Andi Kleen wrote: > > Robert Richter <robert.richter@amd.com> writes: > > > > > Using ALTERNATIVE() when checking for X86_FEATURE_PERFCTR_CORE avoids > > > an extra pointer chase and data cache hit. > > > > Is that really a performance critical path? > > > > Seems more like unnecessary obfuscation to me. > > We hotest path is in perf_pmu_disable(), which happens at least with > every task switch when calling the event scheduler.
Yes but that's already a slow path isn't it? It better is, because the MSR accesses alone are incredibly expensive. I guess your test and jump isn't even on the radar after that ...
-Andi
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