Re: [PATCH] KVM: disable halt_poll_ns as default for s390x

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am 18.09.2015 um 13:29 schrieb Paolo Bonzini:
> 
> 
> On 18/09/2015 12:54, Christian Borntraeger wrote:
>>> -/* halt polling only reduces halt latency by 5-7 us, 500us is enough */
>>> -static unsigned int halt_poll_ns = 500000;
>>> +/* Architectures should define their poll value according to the halt latency */
>>> +static unsigned int halt_poll_ns = KVM_HALT_POLL_NS_DEFAULT;
>>
>> Yes, I prefer this over disabling it via Kconfig. There are benchmarks which
>> benefit from polling on s390. Furthermore it seems that the latency
>> strongly depends on timing of the architecture so making it per arch is
>> probably the right thing to do.
> 
> Perhaps a #ifndef is better than replicating the 500us default in all
> architectures?  Or should the default be 0?

I prefer to not have an ifdef in .c files. I would assume that over time
architectures will provide their own number, e.g. for my uperf cases that
got better, 50000 was enough. 500000 just increased cpu overhead.

Christian