linux-kernel - Re: [RFC PATCH 0/2] sched: simplify the select_task_rq

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Date:	Mon, 21 Jan 2013 15:45:22 +0800
From:	Michael Wang <wangyun@...ux.vnet.ibm.com>
To:	Mike Galbraith <bitbucket@...ine.de>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	peterz@...radead.org, mingo@...nel.org, a.p.zijlstra@...llo.nl
Subject: Re: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()

On 01/21/2013 03:09 PM, Mike Galbraith wrote:
> On Mon, 2013-01-21 at 07:42 +0100, Mike Galbraith wrote: 
>> On Mon, 2013-01-21 at 13:07 +0800, Michael Wang wrote:
> 
>>> May be we could try change this back to the old way later, after the aim
>>> 7 test on my server.
>>
>> Yeah, something funny is going on.
> 
> Never entering balance path kills the collapse.  Asking wake_affine()
> wrt the pull as before, but allowing us to continue should no idle cpu
> be found, still collapsed.  So the source of funny behavior is indeed in
> balance_path.

Below patch based on the patch set could help to avoid enter balance path
if affine_sd could be found, just like the old logical, would you like to
take a try and see whether it could help fix the collapse?

Regards,
Michael Wang

---
 kernel/sched/fair.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d600708..4e95bb0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3297,6 +3297,8 @@ next:
                        sg = sg->next;
                } while (sg != sd->groups);
        }
+
+       return -1;
 done:
        return target;
 }
@@ -3349,7 +3351,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
                 * some cases.
                 */
                new_cpu = select_idle_sibling(p, prev_cpu);
-               if (idle_cpu(new_cpu))
+               if (new_cpu != -1)
                        goto unlock;

                /*
@@ -3363,15 +3365,15 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
                        goto balance_path;

                new_cpu = select_idle_sibling(p, cpu);
-               if (!idle_cpu(new_cpu))
-                       goto balance_path;
-
                /*
                 * Invoke wake_affine() finally since it is no doubt a
                 * performance killer.
                 */
-               if (wake_affine(sbm->affine_map[prev_cpu], p, sync))
-                       goto unlock;
+               if (new_cpu == -1 ||
+                       !wake_affine(sbm->affine_map[prev_cpu], p, sync))
+                       new_cpu = prev_cpu;
+
+               goto unlock;
        }

 balance_path:
-- 
1.7.4.1


> 
> -Mike
> 
> --
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