linux-kernel - Re: [ck] Re: SD still better than CFS for 3d ?(was Re: 2.6.23-rc1)

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Date:	Tue, 31 Jul 2007 16:09:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Miguel Figueiredo <elmig@...ianpt.org>
Cc:	ck@....kolivas.org, Matthew Hawkins <darthmdh@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kasper Sandberg <lkml@...anurb.dk>
Subject: Re: [ck] Re: SD still better than CFS for 3d ?(was Re: 2.6.23-rc1)


* Miguel Figueiredo <elmig@...ianpt.org> wrote:

> CFS does not requeue_task() on SCHED_YIELD (used by graphic drivers) 
> as until 2.6.22 and -ck. [...]

as i pointed it out to you it does, the function's name changed:

 /*
  * sched_yield() support is very simple - we dequeue and enqueue
  */
 static void yield_task_fair(struct rq *rq, struct task_struct *p)
 {
         struct cfs_rq *cfs_rq = task_cfs_rq(p);
         u64 now = __rq_clock(rq);

         /*
          * Dequeue and enqueue the task to update its
          * position within the tree:
          */
         dequeue_entity(cfs_rq, &p->se, 0, now);
         enqueue_entity(cfs_rq, &p->se, 0, now);
 }

plus others have tried the SD NOP-yield hack-patch and while it slightly 
improved the SD numbers it did not change the "CFS is smoother" 
experience.

	Ingo
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