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) /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
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