From: dietmar.eggemann@arm•com (Dietmar Eggemann)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC 0/6] rework sched_domain topology description
Date: Wed, 12 Mar 2014 13:28:07 +0000 [thread overview]
Message-ID: <532060E7.7010203@arm.com> (raw)
In-Reply-To: <20140311131719.GY9987@twins.programming.kicks-ass.net>
On 11/03/14 13:17, Peter Zijlstra wrote:
> On Sat, Mar 08, 2014 at 12:40:58PM +0000, Dietmar Eggemann wrote:
>>>
>>> I don't have a strong opinion about using or not a cpu argument for
>>> setting the flags of a level (it was part of the initial proposal
>>> before we start to completely rework the build of sched_domain)
>>> Nevertheless, I see one potential concern that you can have completely
>>> different flags configuration of the same sd level of 2 cpus.
>>
>> Could you elaborate a little bit further regarding the last sentence? Do you
>> think that those completely different flags configuration would make it
>> impossible, that the load-balance code could work at all at this sd?
>
> So a problem with such an interfaces is that is makes it far too easy to
> generate completely broken domains.
I see the point. What I'm still struggling with is to understand why
this interface is worse then the one where we set-up additional,
adjacent sd levels with new cpu_foo_mask functions plus different static
sd-flags configurations and rely on the sd degenerate functionality in
the core scheduler to fold these levels together to achieve different
per cpu sd flags configurations.
IMHO, exposing struct sched_domain_topology_level bar_topology[] to the
arch is the reason why the core scheduler has to check if the arch
provides a sane sd setup in both cases.
>
> You can, for two cpus in the same domain provide, different flags; such
> a configuration doesn't make any sense at all.
>
> Now I see why people would like to have this; but unless we can make it
> robust I'd be very hesitant to go this route.
>
By making it robust, I guess you mean that the core scheduler has to
check that the provided set-ups are sane, something like the following
code snippet in sd_init()
if (WARN_ONCE(tl->sd_flags & ~TOPOLOGY_SD_FLAGS,
"wrong sd_flags in topology description\n"))
tl->sd_flags &= ~TOPOLOGY_SD_FLAGS;
but for per cpu set-up's.
Obviously, this check has to be in sync with the usage of these flags in
the core scheduler algorithms. This comprises probably that a subset of
these topology sd flags has to be set for all cpus in a sd level whereas
other can be set only for some cpus.
>
>
next prev parent reply other threads:[~2014-03-12 13:28 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-05 7:18 [RFC 0/6] rework sched_domain topology description Vincent Guittot
2014-03-05 7:18 ` [PATCH 2/6] sched: rework of sched_domain topology definition Vincent Guittot
2014-03-05 17:09 ` Dietmar Eggemann
2014-03-06 8:32 ` Vincent Guittot
2014-03-11 10:31 ` Peter Zijlstra
2014-03-11 13:27 ` Vincent Guittot
2014-03-11 13:48 ` Dietmar Eggemann
[not found] ` <1394003906-11630-7-git-send-email-vincent.guittot@linaro.org>
2014-03-05 22:38 ` [RFC 6/6] sched: ARM: create a dedicated scheduler topology table Dietmar Eggemann
2014-03-06 8:42 ` Vincent Guittot
2014-03-05 23:17 ` [RFC 0/6] rework sched_domain topology description Dietmar Eggemann
2014-03-06 9:04 ` Vincent Guittot
2014-03-06 12:31 ` Dietmar Eggemann
2014-03-07 2:47 ` Vincent Guittot
2014-03-08 12:40 ` Dietmar Eggemann
2014-03-10 13:21 ` Vincent Guittot
2014-03-11 13:17 ` Peter Zijlstra
2014-03-12 13:28 ` Dietmar Eggemann [this message]
2014-03-12 13:47 ` Vincent Guittot
2014-03-13 14:07 ` Dietmar Eggemann
2014-03-17 11:52 ` Peter Zijlstra
2014-03-19 19:15 ` Dietmar Eggemann
2014-03-20 8:28 ` Vincent Guittot
2014-03-11 13:08 ` Peter Zijlstra
[not found] ` <1394003906-11630-5-git-send-email-vincent.guittot@linaro.org>
2014-03-11 10:08 ` [RFC 4/6] sched: powerpc: create a dedicated topology table Preeti U Murthy
2014-03-11 13:18 ` Vincent Guittot
2014-03-12 4:42 ` Preeti U Murthy
2014-03-12 7:44 ` Vincent Guittot
2014-03-12 11:04 ` Dietmar Eggemann
2014-03-14 2:30 ` Preeti U Murthy
2014-03-14 2:14 ` Preeti U Murthy
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=532060E7.7010203@arm.com \
--to=dietmar.eggemann@arm$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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