Am 09.04.20 um 15:25 schrieb
Lucas Stach:
> Am Donnerstag, den 09.04.2020, 14:35 +0200
schrieb Christian König:
>> Am 09.04.20 um 03:31 schrieb xinhui pan:
>>> The delayed delete list is per device
which might be very huge. And in
>>> a heavy workload test, the list might
always not be empty. That will
>>> trigger any RCU stall warnings or
softlockups in non-preemptible kernels
>>> Lets do schedule out if possible in that
case.
>> Mhm, I'm not sure if that is actually
allowed. This is called from a
>> work item and those are not really supposed
to be scheduled away.
> Huh? Workitems can schedule out just fine,
otherwise they would be
> horribly broken when it comes to sleeping locks.
Let me refine the sentence: Work items are not really
supposed to be
scheduled purposely. E.g. you shouldn't call
schedule() or
cond_resched() like in the case here.
Getting scheduled away because we wait for a lock is
of course perfectly
fine.
> The workqueue code
> even has measures to keep the workqueues at the
expected concurrency
> level by starting other workitems when one of
them goes to sleep.
Yeah, and exactly that's what I would say we should
avoid here :)
In other words work items can be scheduled away, but
they should not if
not really necessary (e.g. waiting for a lock).
Otherwise as you said new threads for work item
processing are started
up and I don't think we want that.
Just returning from the work item and waiting for the
next cycle is most
likely the better option.
Regards,
Christian.
>
> Regards,
> Lucas
>
>> Maybe rather change the while into while
(!list_empty(&bdev->ddestroy)
>> && !should_reschedule(0)).
>>
>> Christian.
>>
>>> Signed-off-by: xinhui pan
<xinhui.pan@xxxxxxx>
>>> ---
>>> drivers/gpu/drm/ttm/ttm_bo.c | 1 +
>>> 1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c
b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index 9e07c3f75156..b8d853cab33b 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -541,6 +541,7 @@ static bool
ttm_bo_delayed_delete(struct ttm_bo_device *bdev, bool
remove_all)
>>> }
>>>
>>> ttm_bo_put(bo);
>>> + cond_resched();
>>>
spin_lock(&glob->lru_lock);
>>> }
>>> list_splice_tail(&removed,
&bdev->ddestroy);
>>
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