On 08/10/13 16:13, Raghavendra K T wrote: > On 10/08/2013 08:36 PM, Marc Zyngier wrote: >>>> Just gave it a go, and the results are slightly (but consistently) >>>> worse. Over 10 runs: >>>> >>>> Without RELAX_INTERCEPT: Average run 3.3623s >>>> With RELAX_INTERCEPT: Average run 3.4226s >>>> >>>> Not massive, but still noticeable. Any clue? >>> >>> Is it a 4x overcommit? Probably we would have hit the code >>> overhead if it were small guests. >> >> Only 2x overcommit (dual core host, quad vcpu guests). > > Okay. quad vcpu seem to explain. > >> >>> RELAX_INTERCEPT is worth enabling for large guests with >>> overcommits. >> >> I'll try something more aggressive as soon as I get the time. What do >> you call a large guest? So far, the hard limit on ARM is 8 vcpus. >> > > Okay. I was referring to guests >= 32 vcpus. > May be 8vcpu guests with 2x/4x is worth trying. If we still do not > see benefit, then it is not worth enabling. I've just tried with the worse case I can construct, which is a 8 vcpu guest limited to one physical CPU: Over 10 runs: Without RELAX_INTERCEPT: Time: 6.793 Time: 7.619 Time: 6.690 Time: 7.198 Time: 7.659 Time: 7.054 Time: 7.728 Time: 8.546 Time: 7.306 Time: 7.219 Average: 7.381 With RELAX_INTERCEPT: Time: 6.850 Time: 6.889 Time: 7.170 Time: 6.938 Time: 6.756 Time: 7.341 Time: 6.707 Time: 7.452 Time: 6.617 Time: 8.095 Average: 7.082 We're now starting to see some (small) benefits: slightly faster with RELAX_INTERCEPT, and less jitter (the heuristic is better at picking the target vcpu than the default behaviour). I'll enable it in the next version of the series. Thanks! M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
