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Date: Mon, 21 Jan 2013 10:44:56 +0100
From: Mike Galbraith <bitbucket@...ine.de>
To: Michael Wang <wangyun@...ux.vnet.ibm.com>
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 Mon, 2013-01-21 at 17:22 +0800, Michael Wang wrote:
> On 01/21/2013 05:09 PM, Mike Galbraith wrote:
> > On Mon, 2013-01-21 at 15:45 +0800, Michael Wang wrote:
> >> 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?
> >
> > No, it does not.
>
> Hmm...what have changed now compared to the old logical?
What I did earlier to confirm the collapse originates in balance_path is
below. I just retested to confirm.
Tasks jobs/min jti jobs/min/task real cpu
1 435.34 100 435.3448 13.92 3.76 Mon Jan 21 10:24:00 2013
1 440.09 100 440.0871 13.77 3.76 Mon Jan 21 10:24:22 2013
1 440.41 100 440.4070 13.76 3.75 Mon Jan 21 10:24:45 2013
5 2467.43 99 493.4853 12.28 10.71 Mon Jan 21 10:24:59 2013
5 2445.52 99 489.1041 12.39 10.98 Mon Jan 21 10:25:14 2013
5 2475.49 99 495.0980 12.24 10.59 Mon Jan 21 10:25:27 2013
10 4963.14 99 496.3145 12.21 20.64 Mon Jan 21 10:25:41 2013
10 4959.08 99 495.9083 12.22 21.26 Mon Jan 21 10:25:54 2013
10 5415.55 99 541.5550 11.19 11.54 Mon Jan 21 10:26:06 2013
20 9934.43 96 496.7213 12.20 33.52 Mon Jan 21 10:26:18 2013
20 9950.74 98 497.5369 12.18 36.52 Mon Jan 21 10:26:31 2013
20 9893.88 96 494.6939 12.25 34.39 Mon Jan 21 10:26:43 2013
40 18937.50 98 473.4375 12.80 84.74 Mon Jan 21 10:26:56 2013
40 18996.87 98 474.9216 12.76 88.64 Mon Jan 21 10:27:09 2013
40 19146.92 98 478.6730 12.66 89.98 Mon Jan 21 10:27:22 2013
80 37610.55 98 470.1319 12.89 112.01 Mon Jan 21 10:27:35 2013
80 37321.02 98 466.5127 12.99 114.21 Mon Jan 21 10:27:48 2013
80 37610.55 98 470.1319 12.89 111.77 Mon Jan 21 10:28:01 2013
160 69109.05 98 431.9316 14.03 156.81 Mon Jan 21 10:28:15 2013
160 69505.38 98 434.4086 13.95 155.33 Mon Jan 21 10:28:29 2013
160 69207.71 98 432.5482 14.01 155.79 Mon Jan 21 10:28:43 2013
320 108033.43 98 337.6045 17.95 314.01 Mon Jan 21 10:29:01 2013
320 108577.83 98 339.3057 17.86 311.79 Mon Jan 21 10:29:19 2013
320 108395.75 98 338.7367 17.89 312.55 Mon Jan 21 10:29:37 2013
640 151440.84 98 236.6263 25.61 620.37 Mon Jan 21 10:30:03 2013
640 151440.84 97 236.6263 25.61 621.23 Mon Jan 21 10:30:29 2013
640 151145.75 98 236.1652 25.66 622.35 Mon Jan 21 10:30:55 2013
1280 190117.65 98 148.5294 40.80 1228.40 Mon Jan 21 10:31:36 2013
1280 189977.96 98 148.4203 40.83 1229.91 Mon Jan 21 10:32:17 2013
1280 189560.12 98 148.0938 40.92 1231.71 Mon Jan 21 10:32:58 2013
2560 217857.04 98 85.1004 71.21 2441.61 Mon Jan 21 10:34:09 2013
2560 217338.19 98 84.8977 71.38 2448.76 Mon Jan 21 10:35:21 2013
2560 217795.87 97 85.0765 71.23 2443.12 Mon Jan 21 10:36:32 2013
That was with your change backed out, and the q/d below applied.
---
kernel/sched/fair.c | 27 ++++++---------------------
1 file changed, 6 insertions(+), 21 deletions(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3337,6 +3337,8 @@ select_task_rq_fair(struct task_struct *
goto unlock;
if (sd_flag & SD_BALANCE_WAKE) {
+ new_cpu = prev_cpu;
+
/*
* Tasks to be waked is special, memory it relied on
* may has already been cached on prev_cpu, and usually
@@ -3348,33 +3350,16 @@ select_task_rq_fair(struct task_struct *
* from top to bottom, which help to reduce the chance in
* some cases.
*/
- new_cpu = select_idle_sibling(p, prev_cpu);
+ new_cpu = select_idle_sibling(p, new_cpu);
if (idle_cpu(new_cpu))
goto unlock;
- /*
- * No idle cpu could be found in the topology of prev_cpu,
- * before jump into the slow balance_path, try search again
- * in the topology of current cpu if it is the affine of
- * prev_cpu.
- */
- if (!sbm->affine_map[prev_cpu] ||
- !cpumask_test_cpu(cpu, tsk_cpus_allowed(p)))
- goto balance_path;
-
- new_cpu = select_idle_sibling(p, cpu);
- if (!idle_cpu(new_cpu))
- goto balance_path;
+ if (wake_affine(sbm->affine_map[cpu], p, sync))
+ new_cpu = select_idle_sibling(p, cpu);
- /*
- * Invoke wake_affine() finally since it is no doubt a
- * performance killer.
- */
- if (wake_affine(sbm->affine_map[prev_cpu], p, sync))
- goto unlock;
+ goto unlock;
}
-balance_path:
new_cpu = (sd_flag & SD_BALANCE_WAKE) ? prev_cpu : cpu;
sd = sbm->sd[type][sbm->top_level[type]];
--
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