Am 28.11.2014 um 11:08 schrieb Raghavendra KT: > Was able to test the patch, here is the result: I have not tested with > bigger VMs though. Results make it difficult to talk about any side > effect of > patch if any.
Thanks a log. If our assumption is correct, then this patch should have no side effect on x86. Do you have any confidence guess if the numbers below mean: no-change vs. regression vs improvement? Christian > > System 16 core 32cpu (+ht) sandybridge > with 4 guests of 16vcpu each > > +-----------+-----------+-----------+------------+-----------+ > kernbench (time taken lower is better) > +-----------+-----------+-----------+------------+-----------+ > base %stdev patched %stdev %improvement > +-----------+-----------+-----------+------------+-----------+ > 1x 53.1421 2.3086 54.6671 2.9673 -2.86966 > 2x 89.6858 6.4540 94.0626 6.8317 -4.88015 > +-----------+-----------+-----------+------------+-----------+ > > +-----------+-----------+-----------+------------+-----------+ > ebizzy (recors/sec higher is better) > +-----------+-----------+-----------+------------+-----------+ > base %stdev patched %stdev %improvement > +-----------+-----------+-----------+------------+-----------+ > 1x 14523.2500 8.4388 14928.8750 3.0478 2.79294 > 2x 3338.8750 1.4592 3270.8750 2.3980 -2.03661 > +-----------+-----------+-----------+------------+-----------+ > +-----------+-----------+-----------+------------+-----------+ > dbench (Throughput higher is better) > +-----------+-----------+-----------+------------+-----------+ > base %stdev patched %stdev %improvement > +-----------+-----------+-----------+------------+-----------+ > 1x 6386.4737 1.0487 6703.9113 1.2298 4.97047 > 2x 2571.4712 1.3733 2571.8175 1.6919 0.01347 > +-----------+-----------+-----------+------------+-----------+ > > Raghu > > On Wed, Nov 26, 2014 at 3:01 PM, Christian Borntraeger > <borntrae...@de.ibm.com> wrote: >> Am 26.11.2014 um 10:23 schrieb David Hildenbrand: >>>> This change is a trade-off. >>>> PRO: This patch would improve the case of preemption on s390. This is >>>> probably a corner case as most distros have preemption off anyway. >>>> CON: The downside is that kvm_vcpu_yield_to is called also from >>>> kvm_vcpu_on_spin. Here we want to avoid the scheduler overhead for a wrong >>>> decision. >>> >>> Won't most of that part be covered by: >>> if (!ACCESS_ONCE(vcpu->preempted)) >> >> Hmm, right. Checking vcpu->preempted and PF_VCPU might boil down to the same. >> Would be good if to have to performance regression test, though. >> >>> >>> vcpu->preempted is only set when scheduled out involuntarily. It is cleared >>> when scheduled in. s390 sets it manually, to speed up waking up a vcpu. >>> >>> So when our task is scheduled in (an PF_VCPU is set), this check will >>> already >>> avoid scheduler overhead in kvm_vcpu_on_spin() or am I missing something? >>> >> >> CC Raghavendra KT. Could be rerun your kernbench/sysbench/ebizzy setup on >> x86 to see if the patch in this thread causes any regression? If think your >> commit 7bc7ae25b143"kvm: Iterate over only vcpus that are preempted" might >> have really made the PF_VCPU check unnecessary >> >> CC Michael Mueller, do we still have our yield performance setup handy to >> check if this patch causes any regression? >> >> >> Christian >> > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
