Messages in this thread | | | From | Vince Weaver <> | Date | Fri, 9 Mar 2018 09:31:11 -0500 (EST) | Subject | Re: [tip:perf/core] perf/x86/intel: Disable userspace RDPMC usage for large PEBS |
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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.
Vince
> Userspace RDPMC cannot possibly work for large PEBS, which was introduced in: > > 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 exception is when the PEBS interrupt threshold is 1, in which > case user-space RDPMC works well even with auto-reload events. > > Signed-off-by: Kan Liang <kan.liang@linux.intel.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Stephane Eranian <eranian@google.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Vince Weaver <vincent.weaver@maine.edu> > Cc: acme@kernel.org > Fixes: b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt handling (large PEBS interrupt threshold)") > Link: http://lkml.kernel.org/r/1518474035-21006-6-git-send-email-kan.liang@linux.intel.com > Signed-off-by: Ingo Molnar <mingo@kernel.org> > --- > arch/x86/events/core.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c > index 00a6251981d2..9c86e10f1196 100644 > --- a/arch/x86/events/core.c > +++ b/arch/x86/events/core.c > @@ -2117,7 +2117,8 @@ static int x86_pmu_event_init(struct perf_event *event) > event->destroy(event); > } > > - if (READ_ONCE(x86_pmu.attr_rdpmc)) > + if (READ_ONCE(x86_pmu.attr_rdpmc) && > + !(event->hw.flags & PERF_X86_EVENT_FREERUNNING)) > event->hw.flags |= PERF_X86_EVENT_RDPMC_ALLOWED; > > return err; >
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