On Tue, Mar 19, 2019 at 09:03:37AM -0700, Andi Kleen wrote: > On Tue, Mar 19, 2019 at 03:47:48PM +0100, Peter Zijlstra wrote: > > On Mon, Mar 18, 2019 at 02:41:25PM -0700, kan.li...@linux.intel.com wrote: > > > From: Kan Liang <kan.li...@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.
Should be doable.. > > > 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) But you unconditionally set the bit when you enable PEBS for the event. So why clear it?
