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Date: Fri, 10 Oct 2014 12:56:14 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: Wanpeng Li <wanpeng.li@linux.intel.com>, Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@arm.com>, Kirill V Tkhai <tkhai@yandex.ru>,
        Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/deadline: do not try to push tasks if pinned task
 switches to dl
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On Fri, Oct 10, 2014 at 06:26:42PM +0800, Wanpeng Li wrote:
> 
> 于 10/10/14, 6:10 PM, Peter Zijlstra 写道:
> >On Fri, Oct 10, 2014 at 10:43:17AM +0800, Wanpeng Li wrote:
> >>As Kirill mentioned(https://lkml.org/lkml/2013/1/29/118):
> >>| If rq has already had 2 or more pushable tasks and we try to add a
> >>| pinned task then call of push_rt_task will just waste a time.
> >>
> >>Just switched pinned task is not able to be pushed. If the rq had had
> >>several dl tasks before they have already been considered as candidates
> >>to be pushed (or pulled). This patch does the same behavior as rt class
> >>which introduced by commit 104479 (sched/rt: Do not try to push tasks
> >>if pinned task switches to RT).
> >Checkpatch rightly complains:
> >
> >ERROR: Please use 12 or more chars for the git commit ID like: 'commit 10447917551e ("sched/rt: Do not try to push tasks if pinned task switches to RT")'
> >#12:
> >which introduced by commit 104479 (sched/rt: Do not try to push tasks
> 
> I also got this warning before send out the patch, however, I check 6 chars
> is enough for this commit. Anyway, I will send a newer version later.

It is currently, it might not be in the future. I've already had hash
collisions with 8 char hashes. And the fact thats it in the changelog
means it can (and therefore) will be referenced at some point in the
future. If by that point there is a collision...