Re: [patch 01/10 v3] raid5: use wake_up_all for overlap waking

[NeilBrown <neilb@suse.de>]

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On Mon, 25 Jun 2012 15:24:48 +0800 Shaohua Li <shli@kernel.org> wrote:

> It's possible several tasks are waiting for stripe overlap. We clear R5_Overlap
> bit and wake_up, but wake_up just wakes one task. So if there are several tasks
> in the wait queue, some tasks will not be woken up even its strip R5_Overlap
> clear. The end result is tasks hang in make_request.
> 
> wake_up_all should not introduce performance issue here, since overlap case is
> rare.

This is not necessary.
wake_up_all is only different from wake_up if WQ_FLAG_EXCLUSIVE it set, e.g.
by prepare_to_wait_exclusive.
As we don't use an exclusive wait to wait on wait_for_overlap, there is no
point in using wake_up_all, wake_up already wakes everything up.

NeilBrown


> 
> Signed-off-by: Shaohua Li <shli@fusionio.com>
> ---
>  drivers/md/raid5.c |   20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> Index: linux/drivers/md/raid5.c
> ===================================================================
> --- linux.orig/drivers/md/raid5.c	2012-06-19 08:11:10.021688417 +0800
> +++ linux/drivers/md/raid5.c	2012-06-19 08:11:29.833439339 +0800
> @@ -1399,7 +1399,7 @@ static void __raid_run_ops(struct stripe
>  		for (i = disks; i--; ) {
>  			struct r5dev *dev = &sh->dev[i];
>  			if (test_and_clear_bit(R5_Overlap, &dev->flags))
> -				wake_up(&sh->raid_conf->wait_for_overlap);
> +				wake_up_all(&sh->raid_conf->wait_for_overlap);
>  		}
>  	put_cpu();
>  }
> @@ -2436,7 +2436,7 @@ handle_failed_stripe(struct r5conf *conf
>  		}
>  
>  		if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
> -			wake_up(&conf->wait_for_overlap);
> +			wake_up_all(&conf->wait_for_overlap);
>  
>  		while (bi && bi->bi_sector <
>  			sh->dev[i].sector + STRIPE_SECTORS) {
> @@ -2474,7 +2474,7 @@ handle_failed_stripe(struct r5conf *conf
>  			bi = sh->dev[i].toread;
>  			sh->dev[i].toread = NULL;
>  			if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
> -				wake_up(&conf->wait_for_overlap);
> +				wake_up_all(&conf->wait_for_overlap);
>  			if (bi) s->to_read--;
>  			while (bi && bi->bi_sector <
>  			       sh->dev[i].sector + STRIPE_SECTORS) {
> @@ -3572,7 +3572,7 @@ static void handle_stripe(struct stripe_
>  	} else if (s.expanded && !sh->reconstruct_state && s.locked == 0) {
>  		clear_bit(STRIPE_EXPAND_READY, &sh->state);
>  		atomic_dec(&conf->reshape_stripes);
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
>  	}
>  
> @@ -4249,7 +4249,7 @@ static sector_t reshape_request(struct m
>  		spin_lock_irq(&conf->device_lock);
>  		conf->reshape_safe = mddev->reshape_position;
>  		spin_unlock_irq(&conf->device_lock);
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
>  	}
>  
> @@ -4340,7 +4340,7 @@ static sector_t reshape_request(struct m
>  		spin_lock_irq(&conf->device_lock);
>  		conf->reshape_safe = mddev->reshape_position;
>  		spin_unlock_irq(&conf->device_lock);
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
>  	}
>  	return reshape_sectors;
> @@ -5718,7 +5718,7 @@ static void end_reshape(struct r5conf *c
>  		smp_wmb();
>  		conf->reshape_progress = MaxSector;
>  		spin_unlock_irq(&conf->device_lock);
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  
>  		/* read-ahead size must cover two whole stripes, which is
>  		 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
> @@ -5776,7 +5776,7 @@ static void raid5_quiesce(struct mddev *
>  
>  	switch(state) {
>  	case 2: /* resume for a suspend */
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  		break;
>  
>  	case 1: /* stop all writes */
> @@ -5792,14 +5792,14 @@ static void raid5_quiesce(struct mddev *
>  		conf->quiesce = 1;
>  		spin_unlock_irq(&conf->device_lock);
>  		/* allow reshape to continue */
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  		break;
>  
>  	case 0: /* re-enable writes */
>  		spin_lock_irq(&conf->device_lock);
>  		conf->quiesce = 0;
>  		wake_up(&conf->wait_for_stripe);
> -		wake_up(&conf->wait_for_overlap);
> +		wake_up_all(&conf->wait_for_overlap);
>  		spin_unlock_irq(&conf->device_lock);
>  		break;
>  	}


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