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@xxxxxxxxxxxxxxx> AuthorDate: Mon, 12 Feb 2018 14:20:35 -0800 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Fri, 9 Mar 2018 08:22:23 +0100 perf/x86/intel: Disable userspace RDPMC usage for large PEBSSo 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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