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Date: Wed, 26 Jun 2013 10:13:08 -0400 From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> To: Gleb Natapov <gleb@...hat.com> Cc: Andrew Jones <drjones@...hat.com>, Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>, habanero@...ux.vnet.ibm.com, mingo@...hat.com, jeremy@...p.org, x86@...nel.org, hpa@...or.com, pbonzini@...hat.com, linux-doc@...r.kernel.org, xen-devel@...ts.xensource.com, peterz@...radead.org, mtosatti@...hat.com, stefano.stabellini@...citrix.com, andi@...stfloor.org, attilio.rao@...rix.com, ouyang@...pitt.edu, gregkh@...e.de, agraf@...e.de, chegu_vinod@...com, torvalds@...ux-foundation.org, avi.kivity@...il.com, tglx@...utronix.de, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, stephan.diestelhorst@....com, riel@...hat.com, virtualization@...ts.linux-foundation.org, srivatsa.vaddagiri@...il.com Subject: Re: [PATCH RFC V9 0/19] Paravirtualized ticket spinlocks On Wed, Jun 26, 2013 at 03:52:40PM +0300, Gleb Natapov wrote: > On Wed, Jun 26, 2013 at 01:37:45PM +0200, Andrew Jones wrote: > > 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. > > > Can be done, but lets understand why ple on is such a big problem. Is it > possible that ple gap and SPIN_THRESHOLD are not tuned properly? It could be, but it also could be a microcode issue. The earlier version of Intel (and AMD) CPUs did not have the best detection mechanism and had a "jitter" to them. The ple gap and ple window values seemed to be choosen based on microbenchmark - and while they might work great with Windows type guests - the same is not said about Linux. In which case if you fiddle with the ple gap/window you might incur worst performance with Windows guests :-( Or older Linux guests that use the byte-locking mechanism. Perhaps the best option is to introduce - as a seperate patchset - said dynamic window which will be off when pvticket lock is off - and then based on further CPUs improvements, can turn it on/off? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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