linux-kernel - Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios in PLE handler

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Date:	Thu, 27 Sep 2012 12:44:28 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Andrew Jones <drjones@...hat.com>
CC:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	dlaor@...hat.com, Chegu Vinod <chegu_vinod@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler

On 09/27/2012 12:28 PM, Andrew Jones wrote:

>> No, I am not there yet.
>> 
>> So In summary, we are suffering with inconsistent benchmark result,
>> while measuring the benefit of our improvement in PLE/pvlock etc..
> 
> Are you measuring the combined throughput of all running guests, or
> just looking at the results of the benchmarks in a single test guest?
> 
> I've done some benchmarking as well and my stddevs look pretty good for
> kcbench, ebizzy, dbench, and sysbench-memory. I do 5 runs for each
> overcommit level (1.0 - 3.0, stepped by .25 or .5), and 2 runs of that
> full sequence of tests (one with the overcommit levels in scrambled
> order). The relative stddevs for each of the sets of 5 runs look pretty
> good, and the data for the 2 runs match nicely as well.
> 
> To try and get consistent results I do the following 
> - interleave the memory of all guests across all numa nodes on the
>   machine
> - echo 0 > /proc/sys/kernel/randomize_va_space on both host and test
>   guest
> - echo 3 > /proc/sys/vm/drop_caches on both host and test guest before
>   each run
> - use a ramdisk for the benchmark output files on all running guests
> - no periodically running services installed on the test guest
> - HT is turned off as you do, although I'd like to try running again
>   with it turned back on
> 
> Although, I still need to run again measuring the combined throughput
> of all running vms (including the ones launched just to generate busy
> vcpus). Maybe my results won't be as consistent then...
> 


Another way to test is to execute

 perf stat -e 'kvm_exit exit_reason==40' sleep 10

to see how many PAUSEs were intercepted in a given time (except I just
invented the filter syntax).  The fewer we get, the more useful work the
system does.  This ignores kvm_vcpu_on_spin overhead though, so it's
just a rough measure.

-- 
error compiling committee.c: too many arguments to function
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