Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair()
From: Wanpeng Li
Date: Tue Sep 08 2015 - 02:56:03 EST
On 9/8/15 10:10 AM, Byungchul Park wrote:
hello wanpeng,
On Mon, Sep 07, 2015 at 05:45:20PM +0800, Wanpeng Li wrote:
The sleeper task will be normalized when moved from fair_sched_class, in
order that vruntime will be adjusted either the task is running or sleeping
when moved back. The nomalization in switch_to_fair for sleep task will
result in lose fair sleeper bonus in place_entity() once the vruntime -
cfs_rq->min_vruntime is big when moved from fair_sched_class.
it is nothing to do with normalization.
if vruntime - cfs_rq->min_vruntime is big even though place_entity() was
called when moved from fair class, then we actually expect that it still has
a big vruntime when moved back to fair class.
if we don't expect that it still has a big vruntime when moved back to fair
class, we need to consider other approaches e.g. to move a position calling
place_entity() or to add place_entity() call properly ..
however we should not touch normalization logic. in other words, if we
normalized the vruntime when leaved, then we should necessarily restore the
vruntime to a non-normalized value when moved back.
Not about vruntime - cfs_rq->min_vruntime is big, I think my patch
description above is confusing, and what's wrong I found is explained in
the mail which reply to Peterz.
This patch fix it by adjusting vruntime just during migrating as original
codes since the vruntime of the task has usually NOT been normalized in
this case.
could you explain this in detail? when is a vruntime not normalized?
The comments in task_move_group_fair() which you removed in your commit:
| * When !queued, vruntime of the task has usually NOT been normalized
Regards,
Wanpeng Li
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