Messages in this thread | | | Date | Wed, 20 Dec 2017 13:41:47 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH V2 4/4] perf/x86: fix: disable userspace RDPMC usage for large PEBS |
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On Wed, Dec 20, 2017 at 11:42:51AM -0800, kan.liang@linux.intel.com wrote: > From: Kan Liang <kan.liang@linux.intel.com> > > The userspace RDPMC usage never works for large PEBS since the large > PEBS is introduced by > commit b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt > handling (large PEBS interrupt threshold)") > > When the PEBS interrupt threshold is larger than one, there is no way to > get exact auto-reload times and value for userspace RDPMC. > > Disable the userspace RDPMC usage when large PEBS is enabled.
The only drawback is that the event wraps quickly. I suspect in many cases it's still usable for measuring short regions.
I wouldn't force disable it, just let the users deal with it.
-Andi
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