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SubjectRe: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks
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.
>>
>
> 3 guests 8GB RAM, 1 used for kernbench
> (kernbench -f -H -M -o 20) other for cpuhog (shell script with while
> true do hackbench)
>
> 1x: no hogs
> 2x: 8hogs in one guest
> 3x: 8hogs each in two guest
>
> kernbench on PLE:
> Machine : IBM xSeries with Intel(R) Xeon(R) X7560 2.27GHz CPU with 32
> core, with 8 online cpus and 4*64GB RAM.
>
> The average is taken over 4 iterations with 3 run each (4*3=12). and
> stdev is calculated over mean reported in each run.
>
>
> A): 8 vcpu guest
>
> BASE BASE+patch %improvement w.r.t
> mean (sd) mean (sd) patched kernel time
> case 1*1x: 61.7075 (1.17872) 60.93 (1.475625) 1.27605
> case 1*2x: 107.2125 (1.3821349) 97.506675 (1.3461878) 9.95401
> case 1*3x: 144.3515 (1.8203927) 138.9525 (0.58309319) 3.8855
>
>
> B): 16 vcpu guest
> BASE BASE+patch %improvement w.r.t
> mean (sd) mean (sd) patched kernel time
> case 2*1x: 70.524 (1.5941395) 69.68866 (1.9392529) 1.19867
> case 2*2x: 133.0738 (1.4558653) 124.8568 (1.4544986) 6.58114
> case 2*3x: 206.0094 (1.3437359) 181.4712 (2.9134116) 13.5218
>
> B): 32 vcpu guest
> BASE BASE+patch %improvementw.r.t
> mean (sd) mean (sd) patched kernel time
> case 4*1x: 100.61046 (2.7603485) 85.48734 (2.6035035) 17.6905
>
> It seems while we do not see any improvement in low contention case,
> the benefit becomes evident with overcommit and large guests. I am
> continuing analysis with other benchmarks (now with pgbench to check if
> it has acceptable improvement/degradation in low contenstion case).

Here are the results for pgbench and sysbench. Here the results are on a
single guest.

Machine : IBM xSeries with Intel(R) Xeon(R) X7560 2.27GHz CPU with 32
core, with 8
online cpus and 4*64GB RAM.

Guest config: 8GB RAM

pgbench
==========
unit=tps (higher is better)
pgbench based on pgsql 9.2-dev:
http://www.postgresql.org/ftp/snapshot/dev/ (link given by Attilo)

tool used to collect benachmark:
git://git.postgresql.org/git/pgbench-tools.git
config: MAX_WORKER=16 SCALE=32 run for NRCLIENTS = 1, 8, 64

Average taken over 10 iterations.

8 vcpu guest

N base patch improvement
1 5271 5235 -0.687679
8 37953 38202 0.651798
64 37546 37774 0.60359


16 vcpu guest

N base patch improvement
1 5229 5239 0.190876
8 34908 36048 3.16245
64 51796 52852 1.99803

sysbench
==========
sysbench 0.4.12 cnfigured for postgres driver ran with
sysbench --num-threads=8/16/32 --max-requests=100000 --test=oltp
--oltp-table-size=500000 --db-driver=pgsql --oltp-read-only run
annalysed with ministat with
x patch
+ base
8 vcpu guest
---------------
1) num_threads = 8
N Min Max Median Avg Stddev
x 10 20.7805 21.55 20.9667 21.03502 0.22682186
+ 10 21.025 22.3122 21.29535 21.41793 0.39542349
Difference at 98.0% confidence
1.82035% +/- 1.74892%
2) num_threads = 16
N Min Max Median Avg Stddev
x 10 20.8786 21.3967 21.1566 21.14441 0.15490983
+ 10 21.3992 21.9437 21.46235 21.58724 0.2089425
Difference at 98.0% confidence
2.09431% +/- 0.992732%

3) num_threads = 32
N Min Max Median Avg Stddev
x 10 21.1329 21.3726 21.33415 21.2893 0.08324195
+ 10 21.5692 21.8966 21.6441 21.65679 0.093430003
Difference at 98.0% confidence
1.72617% +/- 0.474343%


16 vcpu guest
---------------
1) num_threads = 8
N Min Max Median Avg Stddev
x 10 23.5314 25.6118 24.76145 24.64517 0.74856264
+ 10 22.2675 26.6204 22.9131 23.50554 1.345386
No difference proven at 98.0% confidence
2) num_threads = 16
N Min Max Median Avg Stddev
x 10 12.0095 12.2305 12.15575 12.13926 0.070872722
+ 10 11.413 11.6986 11.4817 11.493 0.080007819
Difference at 98.0% confidence
-5.32372% +/- 0.710561%

3) num_threads = 32
N Min Max Median Avg Stddev
x 10 12.1378 12.3567 12.21675 12.22703 0.0670695
+ 10 11.573 11.7438 11.6306 11.64905 0.062780221
Difference at 98.0% confidence
-4.72707% +/- 0.606349%


32 vcpu guest
---------------
1) num_threads = 8
N Min Max Median Avg Stddev
x 10 30.5602 41.4756 37.45155 36.43752 3.5490215
+ 10 21.1183 49.2599 22.60845 29.61119 11.269393
No difference proven at 98.0% confidence
2) num_threads = 16
N Min Max Median Avg Stddev
x 10 12.2556 12.9023 12.4968 12.55764 0.25330459
+ 10 11.7627 11.9959 11.8419 11.86256 0.088563903
Difference at 98.0% confidence
-5.53512% +/- 1.72448%

3) num_threads = 32
N Min Max Median Avg Stddev
x 10 16.8751 17.0756 16.97335 16.96765 0.063197191
+ 10 21.3763 21.8111 21.6799 21.66438 0.13059888
Difference at 98.0% confidence
27.6805% +/- 0.690056%


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).

(IMO with more overcommit/contention, we can get more than 15% for the
benchmarks and we do ).

Please let me know if you have any suggestions for try.
(Currently my PLE machine lease is expired, it may take some time to
comeback :()

Ingo, Avi ?


>
> Avi,
> Can patch series go ahead for inclusion into tree with following
> reasons:
>
> The patch series brings fairness with ticketlock ( hence the
> predictability, since during contention, vcpu trying
> to acqire lock is sure that it gets its turn in less than total number
> of vcpus conntending for lock), which is very much desired irrespective
> of its low benefit/degradation (if any) in low contention scenarios.
>
> Ofcourse ticketlocks had undesirable effect of exploding LHP problem,
> and the series addresses with improvement in scheduling and sleeping
> instead of burning cpu time.
>
> Finally a less famous one, it brings almost PLE equivalent capabilty to
> all the non PLE hardware (TBH I always preferred my experiment kernel to
> be compiled in my pv guest that saves more than 30 min of time for each
> run).



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