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From: Matt Fleming <matt@codeblueprint.co.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, tglx@linutronix.de, riel@redhat.com,
	hpa@zytor.com, efault@gmx.de, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org, lvenanci@redhat.com,
	xiaolong.ye@intel.com, kitsunyan@inbox.ru, clm@fb.com
Subject: Re: hackbench vs select_idle_sibling; was: [tip:sched/core] sched/fair, cpumask: Export for_each_cpu_wrap()
Date: Fri, 19 May 2017 16:00:35 +0100
Message-ID: <20170519150035.GA2879@codeblueprint.co.uk> (raw)
In-Reply-To: <20170517105350.hk5m4h4jb6dfr65a@hirez.programming.kicks-ass.net>

On Wed, 17 May, at 12:53:50PM, Peter Zijlstra wrote:
> 
> Please test..

Results are still coming in but things do look better with your patch
applied.

It does look like there's a regression when running hackbench in
process mode and when the CPUs are not fully utilised, e.g. check this
out:

hackbench-process-pipes
                            4.4.68                     4.4.68                4.4.68                4.4.68
                        sles12-sp3 select-idle-cpu-aggressive for-each-cpu-wrap-fix  latest-hackbench-fix
Amean    1        0.8853 (  0.00%)           1.2160 (-37.35%)      1.0350 (-16.91%)      1.1853 (-33.89%)

This machine has 80 CPUs and that's a 40 process workload.

Here's the key:

select-idle-cpu-aggressive: 4c77b18cf8b7 ("sched/fair: Make select_idle_cpu() more aggressive")
for-each-cpu-wrap-fix: c743f0a5c50f ("sched/fair, cpumask: Export for_each_cpu_wrap()")
latest-hackbench-fix: this patch

But those results definitely look to be an exception. Here's the same
machine running the same number of tasks but with pthreads,

hackbench-thread-pipes
                            4.4.68                     4.4.68                4.4.68                4.4.68
                        sles12-sp3 select-idle-cpu-aggressive for-each-cpu-wrap-fix  latest-hackbench-fix
Amean    1        0.7427 (  0.00%)           0.9760 (-31.42%)      1.1907 (-60.32%)      0.7643 ( -2.92%)

Nice win.

  parent reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-13 13:56 [RFC 0/3] sched/topology: fix sched groups on NUMA machines with mesh topology Lauro Ramos Venancio
2017-04-13 13:56 ` [RFC 1/3] sched/topology: Refactor function build_overlap_sched_groups() Lauro Ramos Venancio
2017-04-13 14:50   ` Rik van Riel
2017-05-15  9:02   ` [tip:sched/core] " tip-bot for Lauro Ramos Venancio
2017-04-13 13:56 ` [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology Lauro Ramos Venancio
2017-04-13 15:16   ` Rik van Riel
2017-04-13 15:48   ` Peter Zijlstra
2017-04-13 20:21     ` Lauro Venancio
2017-04-13 21:06       ` Lauro Venancio
2017-04-13 23:38         ` Rik van Riel
2017-04-14 10:48           ` Peter Zijlstra
2017-04-14 11:38   ` Peter Zijlstra
2017-04-14 12:20     ` Peter Zijlstra
2017-05-15  9:03       ` [tip:sched/core] sched/fair, cpumask: Export for_each_cpu_wrap() tip-bot for Peter Zijlstra
2017-05-17 10:53         ` hackbench vs select_idle_sibling; was: " Peter Zijlstra
2017-05-17 12:46           ` Matt Fleming
2017-05-17 14:49           ` Chris Mason
2017-05-19 15:00           ` Matt Fleming [this message]
2017-06-05 13:00             ` Matt Fleming
2017-06-06  9:21               ` Peter Zijlstra
2017-06-09 17:52                 ` Chris Mason
2017-06-08  9:22           ` [tip:sched/core] sched/core: Implement new approach to scale select_idle_cpu() tip-bot for Peter Zijlstra
2017-04-14 16:58     ` [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology Peter Zijlstra
2017-04-17 14:40       ` Lauro Venancio
2017-04-13 13:56 ` [RFC 3/3] sched/topology: Different sched groups must not have the same balance cpu Lauro Ramos Venancio
2017-04-13 15:27   ` Rik van Riel
2017-04-14 16:49   ` Peter Zijlstra
2017-04-17 15:34     ` Lauro Venancio
2017-04-18 12:32       ` Peter Zijlstra

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