Re: Two identical systems, radically different performance - Mailing list pgsql-performance

On 10/11/2012 04:40 PM, Andrea Suisani wrote:
> On 10/11/2012 04:19 PM, Claudio Freire wrote:
>> On Thu, Oct 11, 2012 at 11:14 AM, Andrea Suisani <sickpig@opinioni.net> wrote:
>>> sorry to come late to the party, but being in a similar condition
>>> I've googled a bit and I've found a way to disable hyperthreading without
>>> the need to reboot the system and entering the bios:
>>>
>>> echo 0 >/sys/devices/system/node/node0/cpuX/online
>>>
>>> where X belongs to 1..(#cores * 2) if hyperthreading is enabled
>>> (cpu0 can't be switched off).
>>>
>>> didn't try myself on live system, but I definitely will
>>> as soon as I have a new machine to test.
>>
>> Question is... will that remove the performance penalty of HyperThreading?
>
> So I've added to my todo list to perform a test to verify this claim :)

done.

in a brief: the box is dell a PowerEdge r720 with 16GB of RAM,
the cpu is a Xeon 5620 with 6 core, the OS is installed on a raid
(sata disk 7.2k rpm) and the PGDATA is on separate RAID 1 array
(sas 15K rpm) and the controller is a PERC H710 (bbwc with a cache
of 512 MB).

Postgres ver 9.2.1 (sorry for not having benchmarked 9.1,
but this what we plan to deploy in production). Both the OS
(Ubuntu 12.04.1) and Postgres had been briefly tuned according
to the usal standards while trying to mimic Craig's configuration
(see specific settings at the bottom).

TPS including connection establishing, pgbench run in a single
thread mode, connection made through unix socket, OS cache dropped
and Postgres restarted for every run.

those are the results:

                HT        HT SYSFS DIS    HT BIOS DISABLE
-c -t     r1   r2   r3    r1   r2   r3    r1   r2   r3
5  20K   1641 1831 1496  2020 1974 2033  2005 1988 1967
10 10K   2161 2134 2136  2277 2252 2216  1854 1824 1810
20 5k    2550 2508 2558  2417 2388 2357  1924 1928 1954
30 3333  2216 2272 2250  2333 2493 2496  1993 2009 2008
40 2.5K  2179 2221 2250  2568 2535 2500  2025 2048 2018
50 2K    2217 2213 2213  2487 2449 2604  2112 2016 2023

Despite the fact the results don't match my expectation
(I suspect that there's something wrong with the PERC
because, having the controller cache enabled make no
difference in terms of TPS), it seems strange that disabling
HT from the bios will give lesser TPS that HT disable through
sysfs interface.

OS conf:

vm.swappiness=0
vm.overcommit_memory=2
vm.dirty_ratio=2
vm.dirty_background_ratio=1
kernel.shmmax=3454820352
kernel.shmall=2048341
/sbin/blockdev --setra 8192 /dev/sdb
$PGDATA is on ext4 (rw,noatime)
Linux cloud 3.2.0-32-generic #51-Ubuntu SMP Wed Sep 26 21:33:09 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
sdb scheduler is [cfq]

DB conf:

max_connections = 100
shared_buffers = 3200MB
work_mem = 30MB
maintenance_work_mem = 800MB
synchronous_commit = off
full_page_writes = off
checkpoint_segments = 40
checkpoint_timeout = 5min
checkpoint_completion_target = 0.9
random_page_cost = 3.5
effective_cache_size = 10GB
log_autovacuum_min_duration = 0
autovacuum_naptime = 5min


Andrea

p.s. as last try in the process of increasing TPS
I've change the scheduler from cfq to deadline
and for -c 5 t 20K I've got r1=3007, r2=2930 and r3=2985.