Re: [PATCH/RFC 2/3] s390/kvm: Platform specific kvm_arch_vcpu_dont_yield

[Michael Mueller <mimu@linux.vnet.ibm.com>]

On Fri, 14 Feb 2014 10:55:31 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 14/02/14 00:32, Paolo Bonzini wrote:
> > Il 13/02/2014 23:54, Christian Borntraeger ha scritto:
> >> We had several variants but in the end we tried to come up with a patch that does not
> >> influence other architectures. Your proposal would certainly be fine for s390,
> >> but what impact does it have on x86, arm, arm64? Will it cause performance regressions?
> > 
> > It may also have the same advantages you got on s390.
> > 
> >> So I think that the patch as is is probably the safest choice until we have some
> >> data from x86, arm, arm64, no?
> > 
> > No, using an existing API is always better than inventing a new one.
> 
> OK. 
> Michael can you rework the series to simply use 
> " if (waitqueue_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)" in kvm_vcpu_on_spin
> 
> and make kvm_arch_vcpu_runnable  kvm_cpu_has_interrupt(vcpu) in s390 code?
> That should be equivalent for s390 with even simpler code.
> It might also help x86 and others.

Ok, I will adapt the patch accordingly...

> 
> 
> > If you post the new patch series, and describe the benchmark you were using, we can reproduce
> > it on x86.
> 
> The benchmark was some workload doing lots of semaphore up/down with hundreds
> of processes. Will see if I can come up with a minimal test.
> 
> 
> 
>