Messages in this thread | | | Date | Tue, 19 Mar 2019 09:03:37 -0700 | From | Andi Kleen <> | Subject | Re: [PATCH 03/22] perf/x86/intel: Support adaptive PEBSv4 |
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On Tue, Mar 19, 2019 at 03:47:48PM +0100, Peter Zijlstra wrote: > On Mon, Mar 18, 2019 at 02:41:25PM -0700, kan.liang@linux.intel.com wrote: > > From: Kan Liang <kan.liang@linux.intel.com> > > > > Adaptive PEBS is a new way to report PEBS sampling information. Instead > > of a fixed size record for all PEBS events it allows to configure the > > PEBS record to only include the information needed. Events can then opt > > in to use such an extended record, or stay with a basic record which > > only contains the IP. > > > > The major new feature is to support LBRs in PEBS record. > > This allows (much faster) large PEBS, while still supporting callstacks > > through callstack LBR. > > Does it also allow normal LBR usage? Or does it have to be callstacks?
It allows normal LBR too. But I would expect callstack to be the most common one. As long as you set a period you can get multi-record PEBS with -g, which has a lot lower lower overhead than using PMIs.
Eventually I hope we can even make multi-record PEBS work in frequency mode by averaging the frequency over multiple records.
> > hwc->config |= ARCH_PERFMON_EVENTSEL_INT; > > + hwc->config &= ~ICL_EVENTSEL_ADAPTIVE; > > Just curious; the way I read the SDM, we could leave this set, is that > correct?
It needs to be cleared to get the basic record (which should be a common case)
-Andi
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