On Tue, Jun 18, 2013 at 11:11 AM, Peter Zijlstra <[email protected]> wrote: > On Wed, Jun 05, 2013 at 04:43:46PM +0200, Stephane Eranian wrote: >> >> This patch fixes a problem with the shared registers mutual >> exclusion code and incremental event scheduling by the >> generic perf_event code. >> >> There was a bug whereby the mutual exclusion on the shared >> registers was not enforced because of incremental scheduling >> abort due to event constraints. >> >> Example on Nehalem: >> group1= ref-cycles,OFFCORE_RESPONSE_0:PF_RFO >> group2= ref-cycles >> >> The ref-cycles event can only be measured by 1 counter. Yet, there >> are 2 instances here. The first group can be scheduled and is committed. >> Then, the generic code tries to schedule group2 and this fails (because >> there is no more counter to support the 2nd instance of ref-cycles). >> >> But in x86_schedule_events() error path, put_event_contraints() is invoked >> on ALL the events and not just the ones that just failed. That causes the >> "lock" on the shared offcore_response MSR to be released. Yet the first group >> is actually scheduled and is exposed to reprogramming of that shared msr by >> the sibling HT thread (when they are shared by HT threads). In other words, >> there is no guarantee on what is measured for the offcore_response event. >> >> This patch fixes the problem by tagging committed events with the >> PERF_X86_EVENT_COMMITTED tag. In the error path of x86_schedule_events(), >> only the events NOT tagged have their constraint released. The tag >> is eventually removed when the event in descheduled. >> >> Example was given with offcore_response but also applies to LBR_SELECT >> and LDLAT shared registers. >> >> Signed-off-by: Stephane Eranian <[email protected]> > > I'm getting conflicts against other patches -- most notably I think the > contraints stack opt from Andrew Hunter. > Yes, that would not surprise me. I wrote this patch without assuming Andrew's patch would be there. But we need to add it. Then we can fix the shared_regs patch.
> I'll try and get Ingo to finally pick up my queued patches so we can > rebase. Ok, thanks. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
