Message-ID: <53FD5D6C.40105@catalyst.net.nz>
Date: Wed, 27 Aug 2014 16:24:12 +1200
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
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To: Josh Berkus <josh@agliodbs.com>,
 Andres Freund <andres@2ndquadrant.com>
CC: Bruce Momjian <bruce@momjian.us>, pgsql-performance@postgresql.org,
 "Graeme B. Bell" <grb@skogoglandskap.no>
Subject: Re: Turn off Hyperthreading! WAS: 60 core performance with
 9.3
References: <53ACB190.2030206@catalyst.net.nz>
 <WM!d3faee1472c3c4b0fa7a14ce4fee2175ef92f1e0d7e7edb62fe3bcc6fa7e486c99870994a65fa43cc61df990ae549575!@asav-2.01.com>
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 <53F4F36E.6050003@agliodbs.com> <20140821024036.GB26706@momjian.us>
 <WM!a6def31edfeb44a0c2b33db4efa373ee781a1b82f342c0a03c2d35e540e65a0434c32d64b1353526644d086f6706ce42!@asav-3.01.com>
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On 26/08/14 10:13, Josh Berkus wrote:
> On 08/22/2014 07:02 AM, Andres Freund wrote:
>> On 2014-08-21 14:02:26 -0700, Josh Berkus wrote:
>>> On 08/20/2014 07:40 PM, Bruce Momjian wrote:
>>>> Not sure how you can make such a blanket statement when so many people
>>>> have tested and shown the benefits of hyper-threading.
>>>
>>> Actually, I don't know that anyone has posted the benefits of HT.
>>> Link?
>>
>> There's definitely cases where it can help. But it's highly workload
>> *and* hardware dependent.
>
> The only cases I've seen where HT can be beneficial is when you have
> large numbers of idle connections.  Then the idle connections can be
> "parked" on the HT virtual cores.  However, even in this case I haven't
> seen a head-to-head performance comparison.
>

I've just had a pair of Crucial m550's arrive, so a bit of benchmarking 
is in order. The results (below) seem to suggest that HT enabled is 
certainly not inhibiting scaling performance for single socket i7's. I 
performed several runs (typical results shown below).

Intel i7-4770 3.4 Ghz, 16G
2x Crucial m550
Ubuntu 14.04
Postgres 9.4 beta2

logging_collector = on
max_connections = 600
shared_buffers = 1GB
wal_buffers = 32MB
checkpoint_segments = 128
effective_cache_size = 10GB

pgbench scale = 300
test duration (each) = 600s

db on 1x m550
xlog on 1x m550

clients |  tps (HT)|  tps (no HT)
--------+----------+-------------
4       |  517     |  520
8       | 1013     |  999
16      | 1938     | 1913
32      | 3574     | 3560
64      | 5873     | 5412
128     | 8351     | 7450
256     | 9426     | 7840
512     | 9357     | 7288


Regards

Mark


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