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SubjectRe: [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks
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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.

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]


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
[PLE hinders pv-ticket improvements, but even with PLE off,
we still off from ideal throughput (somewhere >20000)]


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]


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]

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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