[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] VT-d scalability issue
Espen Skoglund wrote: > 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? Definitely performance will degrade due to IOTLB pressure when there are many VMs which exhausts IOTLB. Randy (Weidong) > > [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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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