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Date:	Fri, 19 Sep 2014 13:46:22 +0100
From:	Juri Lelli <>
To:	Daniel Wagner <>,
	"" <>
CC:	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	Li Zefan <>,
	"" <>
Subject: Re: [PATCH 2/3] sched/deadline: fix bandwidth check/update when migrating
 tasks between exclusive cpusets

Hi Daniel,

On 19/09/14 12:47, Daniel Wagner wrote:
> Hi,
> On 09/19/2014 11:22 AM, Juri Lelli wrote:
>> Exclusive cpusets are the only way users can restrict SCHED_DEADLINE tasks
>> affinity (performing what is commonly called clustered scheduling).
>> Unfortunately, such thing is currently broken for two reasons:
>>  - No check is performed when the user tries to attach a task to
>>    an exlusive cpuset (recall that exclusive cpusets have an
>>    associated maximum allowed bandwidth).
>>  - Bandwidths of source and destination cpusets are not correctly
>>    updated after a task is migrated between them.
>> This patch fixes both things at once, as they are opposite faces
>> of the same coin.
>> The check is performed in cpuset_can_attach(), as there aren't any
>> points of failure after that function. The updated is split in two
>> halves. We first reserve bandwidth in the destination cpuset, after
>> we pass the check in cpuset_can_attach(). And we then release
>> bandwidth from the source cpuset when the task's affinity is
>> actually changed. Even if there can be time windows when sched_setattr()
>> may erroneously fail in the source cpuset, we are fine with it, as
>> we can't perfom an atomic update of both cpusets at once.
>> Reported-by: Daniel Wagner <>
> Ack
> I have no special test for this, I just let my test running which was
> fixed by patch #1. Works fine though. I'll plan to write some test for this.

Ok, thanks. Just mind that the problem fixed by patch 3/3 may sometime
affect this too. I should have definitely put 3/3 on top of the patchset :/.


- Juri

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