Messages in this thread | | | Date | Tue, 10 Jul 2012 13:57:22 +0530 | From | Raghavendra K T <> | Subject | Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler |
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On 07/09/2012 01:25 PM, Christian Borntraeger wrote: > On 09/07/12 08:20, Raghavendra K T wrote: >> Currently Pause Looop Exit (PLE) handler is doing directed yield to a >> random VCPU on PL exit. Though we already have filtering while choosing >> the candidate to yield_to, we can do better. >> >> Problem is, for large vcpu guests, we have more probability of yielding >> to a bad vcpu. We are not able to prevent directed yield to same guy who >> has done PL exit recently, who perhaps spins again and wastes CPU. >> >> Fix that by keeping track of who has done PL exit. So The Algorithm in series >> give chance to a VCPU which has: > > > We could do the same for s390. The appropriate exit would be diag44 (yield to hypervisor). > > Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though. > So there is no win here, but there are other cases were diag44 is used, e.g. cpu_relax. > I have to double check with others, if these cases are critical, but for now, it seems > that your dummy implementation for s390 is just fine. After all it is a no-op until > we implement something. >
Thanks for the review. Nice to know that, patch has potential to help s390 also.
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