lkml.org 
[lkml]   [2007]   [Aug]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: CFS review

* Al Boldi <a1426z@gawab.com> wrote:

> > so could you please re-check chew jitter behavior with the latest
> > kernel? (i've attached the standalone patch below, it will apply
> > cleanly to rc2 too.)
>
> That fixes it, but by reducing granularity ctx is up 4-fold.

ok, great! (the context-switch rate is obviously up.)

> Mind you, it does have an enormous effect on responsiveness, as
> negative nice with small granularity can't hijack the system any more.

ok. i'm glad you like the result :-) This makes reniced X (or any
reniced app) more usable.

> The thing is, this unpredictability seems to exist even at nice level
> 0, but the smaller granularity covers it all up. It occasionally
> exhibits itself as hick-ups during transient heavy workload flux. But
> it's not easily reproducible.

In general, "hickups" can be due to many, many reasons. If a task got
indeed delayed by scheduling jitter that is provable, even if the
behavior is hard to reproduce, by enabling CONFIG_SCHED_DEBUG=y and
CONFIG_SCHEDSTATS=y in your kernel. First clear all the stats:

for N in /proc/*/task/*/sched; do echo 0 > $N; done

then wait for the 'hickup' to happen, and once it happens capture the
system state (after the hickup) via this script:

http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh

and tell me which specific task exhibited that 'hickup' and send me the
debug output. Also, could you try the patch below as well? Thanks,

Ingo

-------------------------------->
Subject: sched: fix sleeper bonus
From: Ingo Molnar <mingo@elte.hu>

Peter Ziljstra noticed that the sleeper bonus deduction code
was not properly rate-limited: a task that scheduled more
frequently would get a disproportionately large deduction.
So limit the deduction to delta_exec.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched_fair.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -75,7 +75,7 @@ enum {

unsigned int sysctl_sched_features __read_mostly =
SCHED_FEAT_FAIR_SLEEPERS *1 |
- SCHED_FEAT_SLEEPER_AVG *1 |
+ SCHED_FEAT_SLEEPER_AVG *0 |
SCHED_FEAT_SLEEPER_LOAD_AVG *1 |
SCHED_FEAT_PRECISE_CPU_LOAD *1 |
SCHED_FEAT_START_DEBIT *1 |
@@ -304,11 +304,9 @@ __update_curr(struct cfs_rq *cfs_rq, str
delta_mine = calc_delta_mine(delta_exec, curr->load.weight, lw);

if (cfs_rq->sleeper_bonus > sysctl_sched_granularity) {
- delta = calc_delta_mine(cfs_rq->sleeper_bonus,
- curr->load.weight, lw);
- if (unlikely(delta > cfs_rq->sleeper_bonus))
- delta = cfs_rq->sleeper_bonus;
-
+ delta = min(cfs_rq->sleeper_bonus, (u64)delta_exec);
+ delta = calc_delta_mine(delta, curr->load.weight, lw);
+ delta = min((u64)delta, cfs_rq->sleeper_bonus);
cfs_rq->sleeper_bonus -= delta;
delta_mine -= delta;
}
@@ -521,6 +519,8 @@ static void __enqueue_sleeper(struct cfs
* Track the amount of bonus we've given to sleepers:
*/
cfs_rq->sleeper_bonus += delta_fair;
+ if (unlikely(cfs_rq->sleeper_bonus > sysctl_sched_runtime_limit))
+ cfs_rq->sleeper_bonus = sysctl_sched_runtime_limit;

schedstat_add(cfs_rq, wait_runtime, se->wait_runtime);
}
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2007-08-12 17:55    [W:0.145 / U:0.828 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site