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From: Bart Van Assche <bart.vanassche@wdc.com>
To: Christopher Lameter <cl@linux.com>, Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-block@vger.kernel.org, cgroups@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linuxfoundation.org>,
	Tejun Heo <tj@kernel.org>, Balbir Singh <bsingharora@gmail.com>,
	Mike Galbraith <efault@gmx.de>, Oliver Yang <yangoliver@me.com>,
	Shakeel Butt <shakeelb@google.com>, xxx xxx <x.qendo@gmail.com>,
	Taras Kondratiuk <takondra@cisco.com>,
	Daniel Walker <danielwa@cisco.com>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Ruslan Ruslichenko <rruslich@cisco.com>,
	kernel-team@fb.com
Subject: Re: [PATCH 0/7] psi: pressure stall information for CPU, memory, and IO
Date: Mon, 14 May 2018 10:35:37 -0700	[thread overview]
Message-ID: <cb81b9f2-a280-d8a9-c720-247fb9f5fa90@wdc.com> (raw)
In-Reply-To: <010001635f4e8be9-94e7be7a-e75c-438c-bffb-5b56301c4c55-000000@email.amazonses.com>

On 05/14/18 08:39, Christopher Lameter wrote:
> On Mon, 7 May 2018, Johannes Weiner wrote:
>> What to make of this number? If CPU utilization is at 100% and CPU
>> pressure is 0, it means the system is perfectly utilized, with one
>> runnable thread per CPU and nobody waiting. At two or more runnable
>> tasks per CPU, the system is 100% overcommitted and the pressure
>> average will indicate as much. From a utilization perspective this is
>> a great state of course: no CPU cycles are being wasted, even when 50%
>> of the threads were to go idle (and most workloads do vary). From the
>> perspective of the individual job it's not great, however, and they
>> might do better with more resources. Depending on what your priority
>> is, an elevated "some" number may or may not require action.
> 
> This looks awfully similar to loadavg. Problem is that loadavg gets
> screwed up by tasks blocked waiting for I/O. Isnt there some way to fix
> loadavg instead?

The following article explains why it probably made sense in 1993 to 
include TASK_UNINTERRUPTIBLE in loadavg and also why this no longer 
makes sense today:

http://www.brendangregg.com/blog/2017-08-08/linux-load-averages.html

Bart.

  reply	other threads:[~2018-05-14 17:36 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-07 21:01 Johannes Weiner
2018-05-07 21:01 ` [PATCH 1/7] mm: workingset: don't drop refault information prematurely Johannes Weiner
2018-05-07 21:01 ` [PATCH 2/7] mm: workingset: tell cache transitions from workingset thrashing Johannes Weiner
2018-05-07 21:01 ` [PATCH 3/7] delayacct: track delays from thrashing cache pages Johannes Weiner
2018-05-07 21:01 ` [PATCH 4/7] sched: loadavg: consolidate LOAD_INT, LOAD_FRAC, CALC_LOAD Johannes Weiner
2018-05-07 21:01 ` [PATCH 5/7] sched: loadavg: make calc_load_n() public Johannes Weiner
2018-05-09  9:49   ` Peter Zijlstra
2018-05-10 13:46     ` Johannes Weiner
2018-05-07 21:01 ` [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
2018-05-08  0:42   ` Randy Dunlap
2018-05-08 14:06     ` Johannes Weiner
2018-05-08  1:35   ` kbuild test robot
2018-05-08  3:04   ` kbuild test robot
2018-05-08 14:05     ` Johannes Weiner
2018-05-09  9:59   ` Peter Zijlstra
2018-05-10 13:49     ` Johannes Weiner
2018-05-09 10:04   ` Peter Zijlstra
2018-05-10 14:10     ` Johannes Weiner
2018-05-09 10:05   ` Peter Zijlstra
2018-05-10 14:13     ` Johannes Weiner
2018-05-09 10:14   ` Peter Zijlstra
2018-05-10 14:18     ` Johannes Weiner
2018-05-09 10:21   ` Peter Zijlstra
2018-05-10 14:24     ` Johannes Weiner
2018-05-09 10:26   ` Peter Zijlstra
2018-05-09 10:46   ` Peter Zijlstra
2018-05-09 11:38     ` Peter Zijlstra
2018-05-10 13:41       ` Johannes Weiner
2018-05-14  8:33         ` Peter Zijlstra
2018-05-09 10:55   ` Peter Zijlstra
2018-05-09 11:03   ` Vinayak Menon
2018-05-23 13:17     ` Johannes Weiner
2018-05-23 13:19       ` Vinayak Menon
2018-06-07  0:46   ` Suren Baghdasaryan
2018-05-07 21:01 ` [PATCH 7/7] psi: cgroup support Johannes Weiner
2018-05-09 11:07   ` Peter Zijlstra
2018-05-10 14:49     ` Johannes Weiner
2018-05-14 15:39 ` [PATCH 0/7] psi: pressure stall information for CPU, memory, and IO Christopher Lameter
2018-05-14 17:35   ` Bart Van Assche [this message]
2018-05-14 18:55   ` Johannes Weiner
2018-05-14 20:15     ` Christopher Lameter
2018-05-26  0:29 ` Suren Baghdasaryan
2018-05-29 18:16   ` Johannes Weiner
2018-05-30 23:32     ` Suren Baghdasaryan

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