Messages in this thread | | | Date | Mon, 09 Jul 2012 09:55:10 +0200 | From | Christian Borntraeger <> | Subject | Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler |
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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
Christian
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