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Date: Wed, 30 May 2012 16:56:12 +0530 From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com> To: Avi Kivity <avi@...hat.com> CC: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Jeremy Fitzhardinge <jeremy@...p.org>, Greg Kroah-Hartman <gregkh@...e.de>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, "H. Peter Anvin" <hpa@...or.com>, Marcelo Tosatti <mtosatti@...hat.com>, X86 <x86@...nel.org>, Gleb Natapov <gleb@...hat.com>, Ingo Molnar <mingo@...hat.com>, Attilio Rao <attilio.rao@...rix.com>, Virtualization <virtualization@...ts.linux-foundation.org>, Xen Devel <xen-devel@...ts.xensource.com>, linux-doc@...r.kernel.org, KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>, Stefano Stabellini <stefano.stabellini@...citrix.com>, Stephan Diestelhorst <stephan.diestelhorst@....com>, LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Thomas Gleixner <tglx@...utronix.de>, "Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com> Subject: Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks On 05/16/2012 08:49 AM, Raghavendra K T wrote: > On 05/14/2012 12:15 AM, Raghavendra K T wrote: >> On 05/07/2012 08:22 PM, Avi Kivity wrote: >> >> I could not come with pv-flush results (also Nikunj had clarified that >> the result was on NOn PLE >> >>> I'd like to see those numbers, then. >>> >>> Ingo, please hold on the kvm-specific patches, meanwhile. [...] > To summarise, > with 32 vcpu guest with nr thread=32 we get around 27% improvement. In > very low/undercommitted systems we may see very small improvement or > small acceptable degradation ( which it deserves). > For large guests, current value SPIN_THRESHOLD, along with ple_window needed some of research/experiment. [Thanks to Jeremy/Nikunj for inputs and help in result analysis ] I started with debugfs spinlock/histograms, and ran experiments with 32, 64 vcpu guests for spin threshold of 2k, 4k, 8k, 16k, and 32k with 1vm/2vm/4vm for kernbench, sysbench, ebizzy, hackbench. [ spinlock/histogram gives logarithmic view of lockwait times ] machine: PLE machine with 32 cores. Here is the result summary. The summary includes 2 part, (1) %improvement w.r.t 2K spin threshold, (2) improvement w.r.t sum of histogram numbers in debugfs (that gives rough indication of contention/cpu time wasted) For e.g 98% for 4k threshold kbench 1 vm would imply, there is a 98% reduction in sigma(histogram values) compared to 2k case Result for 32 vcpu guest ========================== +----------------+-----------+-----------+-----------+-----------+ | Base-2k | 4k | 8k | 16k | 32k | +----------------+-----------+-----------+-----------+-----------+ | kbench-1vm | 44 | 50 | 46 | 41 | | SPINHisto-1vm | 98 | 99 | 99 | 99 | | kbench-2vm | 25 | 45 | 49 | 45 | | SPINHisto-2vm | 31 | 91 | 99 | 99 | | kbench-4vm | -13 | -27 | -2 | -4 | | SPINHisto-4vm | 29 | 66 | 95 | 99 | +----------------+-----------+-----------+-----------+-----------+ | ebizzy-1vm | 954 | 942 | 913 | 915 | | SPINHisto-1vm | 96 | 99 | 99 | 99 | | ebizzy-2vm | 158 | 135 | 123 | 106 | | SPINHisto-2vm | 90 | 98 | 99 | 99 | | ebizzy-4vm | -13 | -28 | -33 | -37 | | SPINHisto-4vm | 83 | 98 | 99 | 99 | +----------------+-----------+-----------+-----------+-----------+ | hbench-1vm | 48 | 56 | 52 | 64 | | SPINHisto-1vm | 92 | 95 | 99 | 99 | | hbench-2vm | 32 | 40 | 39 | 21 | | SPINHisto-2vm | 74 | 96 | 99 | 99 | | hbench-4vm | 27 | 15 | 3 | -57 | | SPINHisto-4vm | 68 | 88 | 94 | 97 | +----------------+-----------+-----------+-----------+-----------+ | sysbnch-1vm | 0 | 0 | 1 | 0 | | SPINHisto-1vm | 76 | 98 | 99 | 99 | | sysbnch-2vm | -1 | 3 | -1 | -4 | | SPINHisto-2vm | 82 | 94 | 96 | 99 | | sysbnch-4vm | 0 | -2 | -8 | -14 | | SPINHisto-4vm | 57 | 79 | 88 | 95 | +----------------+-----------+-----------+-----------+-----------+ result for 64 vcpu guest ========================= +----------------+-----------+-----------+-----------+-----------+ | Base-2k | 4k | 8k | 16k | 32k | +----------------+-----------+-----------+-----------+-----------+ | kbench-1vm | 1 | -11 | -25 | 31 | | SPINHisto-1vm | 3 | 10 | 47 | 99 | | kbench-2vm | 15 | -9 | -66 | -15 | | SPINHisto-2vm | 2 | 11 | 19 | 90 | +----------------+-----------+-----------+-----------+-----------+ | ebizzy-1vm | 784 | 1097 | 978 | 930 | | SPINHisto-1vm | 74 | 97 | 98 | 99 | | ebizzy-2vm | 43 | 48 | 56 | 32 | | SPINHisto-2vm | 58 | 93 | 97 | 98 | +----------------+-----------+-----------+-----------+-----------+ | hbench-1vm | 8 | 55 | 56 | 62 | | SPINHisto-1vm | 18 | 69 | 96 | 99 | | hbench-2vm | 13 | -14 | -75 | -29 | | SPINHisto-2vm | 57 | 74 | 80 | 97 | +----------------+-----------+-----------+-----------+-----------+ | sysbnch-1vm | 9 | 11 | 15 | 10 | | SPINHisto-1vm | 80 | 93 | 98 | 99 | | sysbnch-2vm | 3 | 3 | 4 | 2 | | SPINHisto-2vm | 72 | 89 | 94 | 97 | +----------------+-----------+-----------+-----------+-----------+ From this, value around 4k-8k threshold seem to be optimal one. [ This is amost inline with ple_window default ] (lower the spin threshold, we would cover lesser % of spinlocks, that would result in more halt_exit/wakeups. [ www.xen.org/files/xensummitboston08/LHP.pdf also has good graphical detail on covering spinlock waits ] After 8k threshold, we see no more contention but that would mean we have wasted lot of cpu time in busy waits. Will get a PLE machine again, and 'll continue experimenting with further tuning of SPIN_THRESHOLD. -- 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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