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Date: Thu, 09 Jul 2015 04:45:38 +0200 From: Mike Galbraith <efault@....de> To: Andres Freund <andres@...razel.de> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org> Subject: Re: Significant performance difference for postgres w/o sched_autogroup 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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