On Wed, Jun 26, 2013 at 02:15:26PM +0530, Raghavendra K T wrote: > On 06/25/2013 08:20 PM, Andrew Theurer wrote: > >On Sun, 2013-06-02 at 00:51 +0530, Raghavendra K T wrote: > >>This series replaces the existing paravirtualized spinlock mechanism > >>with a paravirtualized ticketlock mechanism. The series provides > >>implementation for both Xen and KVM. > >> > >>Changes in V9: > >>- Changed spin_threshold to 32k to avoid excess halt exits that are > >> causing undercommit degradation (after PLE handler improvement). > >>- Added kvm_irq_delivery_to_apic (suggested by Gleb) > >>- Optimized halt exit path to use PLE handler > >> > >>V8 of PVspinlock was posted last year. After Avi's suggestions to look > >>at PLE handler's improvements, various optimizations in PLE handling > >>have been tried. > > > >Sorry for not posting this sooner. I have tested the v9 pv-ticketlock > >patches in 1x and 2x over-commit with 10-vcpu and 20-vcpu VMs. I have > >tested these patches with and without PLE, as PLE is still not scalable > >with large VMs. > > > > Hi Andrew, > > Thanks for testing. > > >System: x3850X5, 40 cores, 80 threads > > > > > >1x over-commit with 10-vCPU VMs (8 VMs) all running dbench: > >---------------------------------------------------------- > > Total > >Configuration Throughput(MB/s) Notes > > > >3.10-default-ple_on 22945 5% CPU in host kernel, 2% spin_lock in guests > >3.10-default-ple_off 23184 5% CPU in host kernel, 2% spin_lock in guests > >3.10-pvticket-ple_on 22895 5% CPU in host kernel, 2% spin_lock in guests > >3.10-pvticket-ple_off 23051 5% CPU in host kernel, 2% spin_lock in guests > >[all 1x results look good here] > > Yes. The 1x results look too close > > > > > > >2x over-commit with 10-vCPU VMs (16 VMs) all running dbench: > >----------------------------------------------------------- > > Total > >Configuration Throughput Notes > > > >3.10-default-ple_on 6287 55% CPU host kernel, 17% spin_lock in guests > >3.10-default-ple_off 1849 2% CPU in host kernel, 95% spin_lock in guests > >3.10-pvticket-ple_on 6691 50% CPU in host kernel, 15% spin_lock in guests > >3.10-pvticket-ple_off 16464 8% CPU in host kernel, 33% spin_lock in guests > > I see 6.426% improvement with ple_on > and 161.87% improvement with ple_off. I think this is a very good sign > for the patches > > >[PLE hinders pv-ticket improvements, but even with PLE off, > > we still off from ideal throughput (somewhere >20000)] > > > > Okay, The ideal throughput you are referring is getting around atleast > 80% of 1x throughput for over-commit. Yes we are still far away from > there. > > > > >1x over-commit with 20-vCPU VMs (4 VMs) all running dbench: > >---------------------------------------------------------- > > Total > >Configuration Throughput Notes > > > >3.10-default-ple_on 22736 6% CPU in host kernel, 3% spin_lock in guests > >3.10-default-ple_off 23377 5% CPU in host kernel, 3% spin_lock in guests > >3.10-pvticket-ple_on 22471 6% CPU in host kernel, 3% spin_lock in guests > >3.10-pvticket-ple_off 23445 5% CPU in host kernel, 3% spin_lock in guests > >[1x looking fine here] > > > > I see ple_off is little better here. > > > > >2x over-commit with 20-vCPU VMs (8 VMs) all running dbench: > >---------------------------------------------------------- > > Total > >Configuration Throughput Notes > > > >3.10-default-ple_on 1965 70% CPU in host kernel, 34% spin_lock in guests > >3.10-default-ple_off 226 2% CPU in host kernel, 94% spin_lock in guests > >3.10-pvticket-ple_on 1942 70% CPU in host kernel, 35% spin_lock in guests > >3.10-pvticket-ple_off 8003 11% CPU in host kernel, 70% spin_lock in guests > >[quite bad all around, but pv-tickets with PLE off the best so far. > > Still quite a bit off from ideal throughput] > > This is again a remarkable improvement (307%). > This motivates me to add a patch to disable ple when pvspinlock is on. > probably we can add a hypercall that disables ple in kvm init patch. > but only problem I see is what if the guests are mixed. > > (i.e one guest has pvspinlock support but other does not. Host > supports pv) How about reintroducing the idea to create per-kvm ple_gap,ple_window state. We were headed down that road when considering a dynamic window at one point. Then you can just set a single guest's ple_gap to zero, which would lead to PLE being disabled for that guest. We could also revisit the dynamic window then. drew > > /me thinks > > > > >In summary, I would state that the pv-ticket is an overall win, but the > >current PLE handler tends to "get in the way" on these larger guests. > > > >-Andrew > > > -- 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
