From: Mike Galbraith <efault@gmx.de>
To: Andres Freund <andres@anarazel.de>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: Significant performance difference for postgres w/o sched_autogroup
Date: Thu, 09 Jul 2015 04:45:38 +0200 [thread overview]
Message-ID: <1436409938.3477.31.camel@gmx.de> (raw)
In-Reply-To: <20150708154550.GH340@alap3.anarazel.de>
On Wed, 2015-07-08 at 17:45 +0200, Andres Freund wrote:
> Workload:
>
> postgresql (multi-process via shared memory SQL server) and benchmark
> client (pgbench, multi threaded) running on the same server. Connected
> using unix sockets. The statements are relatively simple (~1.5ms on
> average), forcing frequent back/forth between server processes and
> pgbench threads.
>
> I found that disabling sched_autogroup *significantly* reduces
> throughput. Even when both server and client are started from the same
> terminal and thus should be in the same group!
>
> There's a significant difference in how %sys with autogroups
> enabled/disabled. ~8% v ~27%. That sounds too much.
Seems reasonable to me. 1(tg)/2(tgs) > 1(task)/N(tasks), throughput is
what the server can sustain on its given budget, larger budget means
less client blockage, thus less %sys.
-Mike
next prev parent reply other threads:[~2015-07-09 2:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-08 15:45 Significant performance difference for postgres w/o sched_autogroup Andres Freund
2015-07-09 2:45 ` Mike Galbraith [this message]
2015-07-09 9:28 ` Andres Freund
2015-07-09 10:35 ` Mike Galbraith
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