[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] VT-d scalability issue
Not regarding the other questions/objections in this thread for a moment --- what kind of performance improvments are we talking of here if the vcpus are pinned? Is it close to 1 VM or is there still some performance degradation due to IOTLB pressure? [And talking of IOTLB pressure, why can't Intel document the IOTLB sizes in the chipset docs? Or even better, why can't these values be queried from the chipset?] eSk [Edwin Zhai] > Keir, > I have found a VT-d scalability issue and want to some feed backs. > When I assign a pass-through NIC to a linux VM and increase the num > of VMs, the iperf throughput for each VM drops greatly. Say, start 8 > VM running on a machine with 8 physical cpus, start 8 iperf client > to connect each of them, the final result is only 60% of 1 VM. > Further investigation shows vcpu migration cause "cold" cache for > pass-through domain. following code in vmx_do_resume try to > invalidate orig processor's cache when 14 migration if this domain > has pass-through device and no support for wbinvd vmexit. > 16 if ( has_arch_pdevs(v->domain) && !cpu_has_wbinvd_exiting ) > { > int cpu = v->arch.hvm_vmx.active_cpu; > if ( cpu != -1 ) > on_selected_cpus(cpumask_of_cpu(cpu), wbinvd_ipi, NULL, 1, > } > So we want to pin vcpu to free processor for domains with > pass-through device in creation process, just like what we did for > NUMA system. > What do you think of it? Or have other ideas? > Thanks, > -- > best rgds, > edwin > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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