Re: [MD PATCH 1/1] Use a new variable to count flighting sync requests

[Coly Li <colyli@suse.de>]

On 2017/4/26 下午9:32, Xiao Ni wrote:
> In new barrier codes, raise_barrier waits if conf->nr_pending[idx] is not zero.
> After all the conditions are true, the resync request can go on be handled. But
> it adds conf->nr_pending[idx] again. The next resync request hit the same bucket
> idx need to wait the resync request which is submitted before. The performance
> of resync/recovery is degraded.
> So we should use a new variable to count sync requests which are in flight.
> 
> Suggested-by: Shaohua Li <shli@kernel.org>
> Suggested-by: Coly Li <colyli@suse.de>
> Signed-off-by: Xiao Ni <xni@redhat.com>

Hi Xiao,

The patch looks good to me. But I do have interest to have a look on the
performance number, does this patch help to improve resync throughput ?
Thanks.

Coly Li

> ---
>  drivers/md/raid1.c | 14 +++++++++++---
>  drivers/md/raid1.h |  1 +
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index a34f587..3c304ef 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -869,7 +869,7 @@ static void raise_barrier(struct r1conf *conf, sector_t sector_nr)
>  			     atomic_read(&conf->barrier[idx]) < RESYNC_DEPTH,
>  			    conf->resync_lock);
>  
> -	atomic_inc(&conf->nr_pending[idx]);
> +	atomic_inc(&conf->nr_sync_pending[idx]);
>  	spin_unlock_irq(&conf->resync_lock);
>  }
>  
> @@ -880,7 +880,7 @@ static void lower_barrier(struct r1conf *conf, sector_t sector_nr)
>  	BUG_ON(atomic_read(&conf->barrier[idx]) <= 0);
>  
>  	atomic_dec(&conf->barrier[idx]);
> -	atomic_dec(&conf->nr_pending[idx]);
> +	atomic_dec(&conf->nr_sync_pending[idx]);
>  	wake_up(&conf->wait_barrier);
>  }
>  
> @@ -1018,7 +1018,8 @@ static int get_unqueued_pending(struct r1conf *conf)
>  	int idx, ret;
>  
>  	for (ret = 0, idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
> -		ret += atomic_read(&conf->nr_pending[idx]) -
> +		ret += atomic_read(&conf->nr_pending[idx]) +
> +			atomic_read(&conf->nr_sync_pending[idx]) -
>  			atomic_read(&conf->nr_queued[idx]);
>  
>  	return ret;
> @@ -3024,6 +3025,11 @@ static struct r1conf *setup_conf(struct mddev *mddev)
>  	if (!conf->nr_pending)
>  		goto abort;
>  
> +	conf->nr_sync_pending = kcalloc(BARRIER_BUCKETS_NR,
> +				   sizeof(atomic_t), GFP_KERNEL);
> +	if (!conf->nr_sync_pending)
> +		goto abort;
> +
>  	conf->nr_waiting = kcalloc(BARRIER_BUCKETS_NR,
>  				   sizeof(atomic_t), GFP_KERNEL);
>  	if (!conf->nr_waiting)
> @@ -3136,6 +3142,7 @@ static struct r1conf *setup_conf(struct mddev *mddev)
>  		kfree(conf->mirrors);
>  		safe_put_page(conf->tmppage);
>  		kfree(conf->poolinfo);
> +		kfree(conf->nr_sync_pending);
>  		kfree(conf->nr_pending);
>  		kfree(conf->nr_waiting);
>  		kfree(conf->nr_queued);
> @@ -3241,6 +3248,7 @@ static void raid1_free(struct mddev *mddev, void *priv)
>  	kfree(conf->mirrors);
>  	safe_put_page(conf->tmppage);
>  	kfree(conf->poolinfo);
> +	kfree(conf->nr_sync_pending);
>  	kfree(conf->nr_pending);
>  	kfree(conf->nr_waiting);
>  	kfree(conf->nr_queued);
> diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
> index dd22a37..a3580ee 100644
> --- a/drivers/md/raid1.h
> +++ b/drivers/md/raid1.h
> @@ -85,6 +85,7 @@ struct r1conf {
>  	wait_queue_head_t	wait_barrier;
>  	spinlock_t		resync_lock;
>  	atomic_t		*nr_pending;
> +	atomic_t		*nr_sync_pending;
>  	atomic_t		*nr_waiting;
>  	atomic_t		*nr_queued;
>  	atomic_t		*barrier;
>