Messages in this thread | | | Date | Mon, 16 Jun 2014 11:21:47 -0400 | From | Don Zickus <> | Subject | Re: [PATCH] perf/x86/intel: ignore CondChgd bit to avoid false NMI handling |
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On Thu, Jun 12, 2014 at 09:37:16AM +0200, Peter Zijlstra wrote: > On Thu, Jun 12, 2014 at 04:00:11PM +0900, HATAYAMA Daisuke wrote: > > Also, I checked cpuid on the system with Neharlem processor where I > > have never seen CondChg bit is set. > > > > [root@localhost ~]# ./cpuid -r > > CPU 0: > > 0x00000000 0x00: eax=0x0000000b ebx=0x756e6547 ecx=0x6c65746e edx=0x49656e69 > > 0x00000001 0x00: eax=0x000206e6 ebx=0x40200800 ecx=0x00bce3bd edx=0xbfebfbff > > <snip> > > 0x0000000a 0x00: eax=0x07300403 ebx=0x00000044 ecx=0x00000000 edx=0x00000603 > > ^^^^^^^^^^^^^^ > > So, cpuid tells that CondChg bit is supported on this processor, too. > > Yeah, I can't remember ever seeing that bit on nhm/wsm either. Weird > stuff that. > > > > In any case, the proposed patch seems fine, just needs a better > > > changelog. > > > > > > > I see. > > > > I'll write that the problem is that any NMI could be robbed by NMI > > watchdog explicitly. Now only patch title says this explicitly. This > > is your first comment. > > Yeah, since that is the actual problem, its good to be clear on that. > > > About CondChgd bit, I cannot write more than I see on actual > > system. If it's necessary to describe more about CondChgd bit, it > > would be appreciated if someone tell me more information about it. > > I think we've found all 2 sentences the SDM has about that and unless > someone from Intel is going to come and explain why they wasted precious > silicon on this I suppose it will remain a mystery. No need to update on > that.
Just to add to the mix, we (Red Hat) has a customer with the same problem. I told them to fight it out with Intel to figure out why that bit is non-zero at boot. Partly because I didn't feel like send a patch upstream and feel the wrath of Peter Z. descend upon me. :-)
So if this patch is acceptable, I would ack it as it fixes our customer's problem too.
Cheers, Don
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