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SubjectRe: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected
(Adding everybody to CC and leaving the below for reference.)

Guys,

as Nikolay says below, we have a regression in 3.6 with pgbench's
benchmark in postgresql.

I was able to reproduce it on another box here and did a bisection run.
It pointed to the commit below.

And yes, reverting that commit fixes the issue here.

@Nikolay: can you try reverting it from 3.6-rc5 and check whether the
regression dissapears at your end?

Thanks.

commit 970e178985cadbca660feb02f4d2ee3a09f7fdda
Author: Mike Galbraith <efault@gmx.de>
Date: Tue Jun 12 05:18:32 2012 +0200

sched: Improve scalability via 'CPU buddies', which withstand random perturbations

Traversing an entire package is not only expensive, it also leads to tasks
bouncing all over a partially idle and possible quite large package. Fix
that up by assigning a 'buddy' CPU to try to motivate. Each buddy may try
to motivate that one other CPU, if it's busy, tough, it may then try its
SMT sibling, but that's all this optimization is allowed to cost.

Sibling cache buddies are cross-wired to prevent bouncing.

4 socket 40 core + SMT Westmere box, single 30 sec tbench runs, higher is better:

clients 1 2 4 8 16 32 64 128
..........................................................................
pre 30 41 118 645 3769 6214 12233 14312
post 299 603 1211 2418 4697 6847 11606 14557
A nice increase in performance.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1339471112.7352.32.camel@marge.simpson.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>


On Fri, Sep 14, 2012 at 10:47:44AM +0300, Nikolay Ulyanitsky wrote:
> Hi
> I compiled the 3.6-rc5 kernel with the same config from 3.5.3 and got
> the 15-20% performance drop of PostgreSQL 9.2 on AMD chipsets (880G,
> 990X).
>
> CentOS 6.3 x86_64
> PostgreSQL 9.2
> cpufreq scaling_governor - performance
>
> # /etc/init.d/postgresql initdb
> # echo "fsync = off" >> /var/lib/pgsql/data/postgresql.conf
> # /etc/init.d/postgresql start
> # su - postgres
> $ psql
> # create database pgbench;
> # \q
>
> # pgbench -i pgbench && pgbench -c 10 -t 10000 pgbench
> tps = 4670.635648 (including connections establishing)
> tps = 4673.630345 (excluding connections establishing)[/code]
>
> On kernel 3.5.3:
> tps = ~5800
>
> 1) Host 1 - 15-20% performance drop
> AMD Phenom(tm) II X6 1090T Processor
> MB: AMD 880G
> RAM: 16 Gb DDR3
> SSD: PLEXTOR PX-256M3 256Gb
>
> 2) Host 2 - 15-20% performance drop
> AMD Phenom(tm) II X6 1055T Processor
> MB: AMD 990X
> RAM: 32 Gb DDR3
> SSD: Corsair Performance Pro 128Gb
>
> 3) Host 3 - no problems - same performance
> Intel E6300
> MB: Intel® P43 / ICH10
> RAM: 4 Gb DDR3
> HDD: SATA 7200 rpm
>
> Kernel config - http://pastebin.com/cFpg5JSJ
>
> Any ideas?
>
> Thx
> --
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--
Regards/Gruss,
Boris.
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