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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