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SubjectRE: [rfc patch] Re: sched: incorrect argument used in task_hot()
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Mike Galbraith wrote on Friday, November 17, 2006 2:19 PM
> > And a changelog, then we're all set!
> >
> > Oh. And a patch, too.
>
> Co-opt rq->timestamp_last_tick to maintain a cache_hot_time evaluation
> reference timestamp at both tick and sched times to prevent said
> reference, formerly rq->timestamp_last_tick, from being behind
> task->last_ran at evaluation time, and to move said reference closer to
> current time on the remote processor, intent being to improve cache hot
> evaluation and timestamp adjustment accuracy for task migration.
>
> Fix minor sched_time double accounting error which occurs when a task
> passing through schedule() does not schedule off, and takes the next
> timer tick.
>
> [....]
>
> @@ -2206,7 +2207,7 @@ skip_queue:
> }
>
> #ifdef CONFIG_SCHEDSTATS
> - if (task_hot(tmp, busiest->timestamp_last_tick, sd))
> + if (task_hot(tmp, busiest->most_recent_timestamp, sd))
> schedstat_inc(sd, lb_hot_gained[idle]);
> #endif


While we at it, let's clean up this hunk. task_hot is evaluated twice in
the more common case of nr_balance_failed <= cache_nice_tries. We should
only test/increment relevant stats for forced migration.
Patch on top of yours.


Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>


--- ./kernel/sched.c.orig 2006-11-17 13:37:46.000000000 -0800
+++ ./kernel/sched.c 2006-11-17 14:20:34.000000000 -0800
@@ -2088,8 +2088,13 @@ int can_migrate_task(struct task_struct
* 2) too many balance attempts have failed.
*/

- if (sd->nr_balance_failed > sd->cache_nice_tries)
+ if (sd->nr_balance_failed > sd->cache_nice_tries) {
+ #ifdef CONFIG_SCHEDSTATS
+ if (task_hot(p, rq->most_recent_timestamp, sd))
+ schedstat_inc(sd, lb_hot_gained[idle]);
+ #endif
return 1;
+ }

if (task_hot(p, rq->most_recent_timestamp, sd))
return 0;
@@ -2189,11 +2194,6 @@ skip_queue:
goto skip_bitmap;
}

-#ifdef CONFIG_SCHEDSTATS
- if (task_hot(tmp, busiest->most_recent_timestamp, sd))
- schedstat_inc(sd, lb_hot_gained[idle]);
-#endif
-
pull_task(busiest, array, tmp, this_rq, dst_array, this_cpu);
pulled++;
rem_load_move -= tmp->load_weight;
-
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