From: Vincent Guittot <vincent.guittot@linaro.org>
To: Alex Shi <alex.shi@intel.com>
Cc: "mingo@redhat.com" <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Arjan van de Ven <arjan@linux.intel.com>,
Borislav Petkov <bp@alien8.de>, Paul Turner <pjt@google.com>,
Namhyung Kim <namhyung@kernel.org>,
Mike Galbraith <efault@gmx.de>,
Morten Rasmussen <morten.rasmussen@arm.com>,
gregkh@linuxfoundation.org,
Preeti U Murthy <preeti@linux.vnet.ibm.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Len Brown <len.brown@intel.com>,
rafael.j.wysocki@intel.com, jkosina@suse.cz,
Clark Williams <clark.williams@gmail.com>,
"tony.luck@intel.com" <tony.luck@intel.com>,
keescook@chromium.org, Mel Gorman <mgorman@suse.de>,
riel@redhat.com
Subject: Re: [patch v3 6/8] sched: consider runnable load average in move_tasks
Date: Tue, 9 Apr 2013 13:56:42 +0200 [thread overview]
Message-ID: <CAKfTPtAY3HpFhWiW=-P0_oBss2XhKJYRQJvFHqqapcZ7O0P6kQ@mail.gmail.com> (raw)
In-Reply-To: <5163EF9E.4030005@intel.com>
On 9 April 2013 12:38, Alex Shi <alex.shi@intel.com> wrote:
> On 04/09/2013 04:58 PM, Vincent Guittot wrote:
>>>> >> How do you ensure that runnable_avg_period and runnable_avg_sum are
>>>> >> coherent ? an update of the statistic can occur in the middle of your
>>>> >> sequence.
>>> >
>>> > Thanks for your question, Vincent!
>>> > the runnable_avg_period and runnable_avg_sum, only updated in
>>> > __update_entity_runnable_avg().
>>> > Yes, I didn't see some locks to ensure the coherent of them. but they
>>> > are updated closely, and it is not big deal even a little incorrect to
>>> > their value. These data are collected periodically, don't need very very
>>> > precise at every time.
>>> > Am I right? :)
>> The problem mainly appears during starting phase (the 1st 345ms) when
>> runnable_avg_period has not reached the max value yet so you can have
>> avg.runnable_avg_sum greater than avg.runnable_avg_period. In a worst
>> case, runnable_avg_sum could be twice runnable_avg_period
>
> Oh, That's a serious problem. Do you catch it in real word or in code?
I haven't trace that shows this issue but nothing prevent an update to
occur while you get values so you can have a mix of old and new
values.
> Could you explain more for details?
Both fields of a new task increase simultaneously but if you get the
old value for runnable_avg_period and the new one for
runnable_avg_sum, runnable_avg_sum will be greater than
runnable_avg_period during this starting phase.
The worst case appears 2ms after the creation of the task,
runnable_avg_period and runnable_avg_sum should go from 1024 to 2046.
So the task_h_load_avg will be 199% of task_h_load If you have
runnable_avg_period with 1024 and runnable_avg_sum with 2046.
A simple solution is to check that runnable_avg_period is always
greater or equal to runnable_avg_sum like i have done in my packing
small tasks patches
Vincent
>
> --
> Thanks
> Alex
next prev parent reply other threads:[~2013-04-09 11:56 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-02 3:23 [patch v3 0/8] sched: use runnable avg in load balance Alex Shi
2013-04-02 3:23 ` [patch v3 1/8] Revert "sched: Introduce temporary FAIR_GROUP_SCHED dependency for load-tracking" Alex Shi
2013-04-02 3:23 ` [patch v3 2/8] sched: set initial value of runnable avg for new forked task Alex Shi
2013-04-02 3:23 ` [patch v3 3/8] sched: only count runnable avg on cfs_rq's nr_running Alex Shi
2013-04-03 3:19 ` Alex Shi
2013-04-02 3:23 ` [patch v3 4/8] sched: update cpu load after task_tick Alex Shi
2013-04-02 3:23 ` [patch v3 5/8] sched: compute runnable load avg in cpu_load and cpu_avg_load_per_task Alex Shi
2013-04-02 3:23 ` [patch v3 6/8] sched: consider runnable load average in move_tasks Alex Shi
2013-04-09 7:08 ` Vincent Guittot
2013-04-09 8:05 ` Alex Shi
2013-04-09 8:58 ` Vincent Guittot
2013-04-09 10:38 ` Alex Shi
2013-04-09 11:56 ` Vincent Guittot [this message]
2013-04-09 14:48 ` Alex Shi
2013-04-09 15:16 ` Vincent Guittot
2013-04-10 2:31 ` Alex Shi
2013-04-10 6:07 ` Michael Wang
2013-04-10 6:55 ` Vincent Guittot
2013-04-02 3:23 ` [patch v3 7/8] sched: consider runnable load average in effective_load Alex Shi
2013-04-02 3:23 ` [patch v3 8/8] sched: use instant load for burst wake up Alex Shi
2013-04-02 7:23 ` [patch v3 0/8] sched: use runnable avg in load balance Michael Wang
2013-04-02 8:34 ` Mike Galbraith
2013-04-02 9:13 ` Michael Wang
2013-04-02 8:35 ` Alex Shi
2013-04-02 9:45 ` Michael Wang
2013-04-03 2:46 ` Michael Wang
2013-04-03 2:56 ` Alex Shi
2013-04-03 3:23 ` Michael Wang
2013-04-03 4:28 ` Alex Shi
2013-04-03 5:38 ` Michael Wang
2013-04-03 5:53 ` Michael Wang
2013-04-03 6:01 ` Alex Shi
2013-04-03 6:22 ` Michael Wang
2013-04-03 6:53 ` Alex Shi
2013-04-03 7:18 ` Michael Wang
2013-04-03 7:28 ` Alex Shi
2013-04-03 8:46 ` Alex Shi
2013-04-03 9:37 ` Michael Wang
2013-04-03 11:17 ` Alex Shi
2013-04-07 3:09 ` Michael Wang
2013-04-07 7:30 ` Alex Shi
2013-04-07 8:56 ` Michael Wang
2013-04-09 5:08 ` Alex Shi
2013-04-10 13:12 ` Alex Shi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAKfTPtAY3HpFhWiW=-P0_oBss2XhKJYRQJvFHqqapcZ7O0P6kQ@mail.gmail.com' \
--to=vincent.guittot@linaro.org \
--cc=akpm@linux-foundation.org \
--cc=alex.shi@intel.com \
--cc=arjan@linux.intel.com \
--cc=bp@alien8.de \
--cc=clark.williams@gmail.com \
--cc=efault@gmx.de \
--cc=gregkh@linuxfoundation.org \
--cc=jkosina@suse.cz \
--cc=keescook@chromium.org \
--cc=len.brown@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=morten.rasmussen@arm.com \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
--cc=pjt@google.com \
--cc=preeti@linux.vnet.ibm.com \
--cc=rafael.j.wysocki@intel.com \
--cc=riel@redhat.com \
--cc=tglx@linutronix.de \
--cc=tony.luck@intel.com \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).