On 07/12/2013 08:45 AM, Dave Jones wrote: > On Fri, Jul 12, 2013 at 08:38:52AM -0700, Dave Hansen wrote: > > Dave, for your case, my suspicion would be that it got turned on > > inadvertently, or that we somehow have a bug which bumped up > > perf_event.c's 'active_events' and we're running some perf code that we > > don't have to. > > What do you 'inadvertantly' ? I see this during bootup every time. > Unless systemd or something has started playing with perf, (which afaik it > isn't)
I mean that somebody turned 'active_events' on without actually wanting perf to be on. I'd be curious how it got set to something nonzero. Could you stick a WARN_ONCE() or printk_ratelimit() on the three sites that modify it? > > But, I'm suspicious. I was having all kinds of issues with perf and > > NMIs taking hundreds of milliseconds. I never isolated it to having a > > real, single, cause. I attributed it to my large NUMA system just being > > slow. Your description makes me wonder what I missed, though. > > Here's a fun trick: > > trinity -c perf_event_open -C4 -q -l off > > Within about a minute, that brings any of my boxes to its knees. > The softlockup detector starts going nuts, and then the box wedges solid. On my box, the same happens with 'perf top'. ;) *But* dropping the perf sample rate has been really effective at keeping me from hitting it, and I've had to use _lots_ of CPUs (60-160) doing those NMIs at once to trigger the lockups. Being able to trigger it with so few CPUs is interesting though. I'll try on my hardware. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
