Messages in this thread | | | Subject | Re: [tip:perf/core] perf/x86/intel: Disable userspace RDPMC usage for large PEBS | From | "Liang, Kan" <> | Date | Mon, 12 Mar 2018 10:08:09 -0400 |
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On 3/9/2018 2:10 PM, Vince Weaver wrote: > On Fri, 9 Mar 2018, Peter Zijlstra wrote: > >> On Fri, Mar 09, 2018 at 09:31:11AM -0500, Vince Weaver wrote: >>> On Fri, 9 Mar 2018, tip-bot for Kan Liang wrote: >>> >>>> Commit-ID: 1af22eba248efe2de25658041a80a3d40fb3e92e >>>> Gitweb: https://git.kernel.org/tip/1af22eba248efe2de25658041a80a3d40fb3e92e >>>> Author: Kan Liang <kan.liang@linux.intel.com> >>>> AuthorDate: Mon, 12 Feb 2018 14:20:35 -0800 >>>> Committer: Ingo Molnar <mingo@kernel.org> >>>> CommitDate: Fri, 9 Mar 2018 08:22:23 +0100 >>>> >>>> perf/x86/intel: Disable userspace RDPMC usage for large PEBS >>>> >>> >>> >>> So this whole commit log is about disabling RDPMC usage for "large PEBS" >>> but the actual change disables RDPMC if "PERF_X86_EVENT_FREERUNNING" >>> >>> Either the commit log is really misleading, or else a poor name was chosen >>> for this feature. >> >> Its the same thing, and yes that might want renaming I suppose. > > I apologize for noticing these things so late in the game, but I haven't > had time to keep up with a full lkml feed recently so I only see these > things once I'm CC'd on them. > > So to summarize this: rdpmc is only disabled on a per-event basis, and > only if that event is doing multi-pebs sampling? >
If the event can do multi-pebs sampling, the rdpmc will be disabled. Other events which cannot do multi-pebs will not be impacted.
To enable multi-pebs sampling for event, it requires a fixed period. It doesn't support callgraph. For older platform (before SKL), it doesn't support time stamp.
Thanks, Kan
> If that's true, then I don't think I have an issue with this. > > We finally got rdpmc support in a released PAPI, and it is a massive > improvement when self-monitoring (even moreso if KPTI is enabled) so I was > just trying to make sure this wouldn't suddenly disable rdpmc out from > under us. > > Vince >
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