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Re: [patch 1/8] raid5: add a per-stripe lock | |
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On Mon, 04 Jun 2012 16:01:53 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
> Add a per-stripe lock to protect stripe specific data, like dev->read,
> written, ... The purpose is to reduce lock contention of conf->device_lock.
I'm not convinced that you need to add a lock.
I am convinced that if you do add one you need to explain exactly what it is
protecting.
The STRIPE_ACTIVE bit serves as a lock and ensures that only one process can
be in handle_stripe at a time.
So I don't think dev->read actually needs any protection (though I haven't
checked thoroughly).
I think the only things that device_lock protects are things shared by
multiple stripes, so adding a per-stripe spinlock isn't going to help remove
device_lock.
Thanks,
NeilBrown
>
> Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
> ---
> drivers/md/raid5.c | 17 +++++++++++++++++
> drivers/md/raid5.h | 1 +
> 2 files changed, 18 insertions(+)
>
> Index: linux/drivers/md/raid5.c
> ===================================================================
> --- linux.orig/drivers/md/raid5.c 2012-06-01 13:38:54.705210229 +0800
> +++ linux/drivers/md/raid5.c 2012-06-01 13:43:05.594056130 +0800
> @@ -749,6 +749,7 @@ static void ops_complete_biofill(void *s
>
> /* clear completed biofills */
> spin_lock_irq(&conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> for (i = sh->disks; i--; ) {
> struct r5dev *dev = &sh->dev[i];
>
> @@ -774,6 +775,7 @@ static void ops_complete_biofill(void *s
> }
> }
> }
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
> clear_bit(STRIPE_BIOFILL_RUN, &sh->state);
>
> @@ -798,8 +800,10 @@ static void ops_run_biofill(struct strip
> if (test_bit(R5_Wantfill, &dev->flags)) {
> struct bio *rbi;
> spin_lock_irq(&conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> dev->read = rbi = dev->toread;
> dev->toread = NULL;
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
> while (rbi && rbi->bi_sector <
> dev->sector + STRIPE_SECTORS) {
> @@ -1137,10 +1141,12 @@ ops_run_biodrain(struct stripe_head *sh,
> struct bio *wbi;
>
> spin_lock_irq(&sh->raid_conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> chosen = dev->towrite;
> dev->towrite = NULL;
> BUG_ON(dev->written);
> wbi = dev->written = chosen;
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&sh->raid_conf->device_lock);
>
> while (wbi && wbi->bi_sector <
> @@ -1446,6 +1452,8 @@ static int grow_one_stripe(struct r5conf
> init_waitqueue_head(&sh->ops.wait_for_ops);
> #endif
>
> + spin_lock_init(&sh->stripe_lock);
> +
> if (grow_buffers(sh)) {
> shrink_buffers(sh);
> kmem_cache_free(conf->slab_cache, sh);
> @@ -2327,6 +2335,7 @@ static int add_stripe_bio(struct stripe_
>
>
> spin_lock_irq(&conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> if (forwrite) {
> bip = &sh->dev[dd_idx].towrite;
> if (*bip == NULL && sh->dev[dd_idx].written == NULL)
> @@ -2360,6 +2369,7 @@ static int add_stripe_bio(struct stripe_
> if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
> set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
> }
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
>
> pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
> @@ -2376,6 +2386,7 @@ static int add_stripe_bio(struct stripe_
>
> overlap:
> set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
> return 0;
> }
> @@ -2427,6 +2438,7 @@ handle_failed_stripe(struct r5conf *conf
> }
> }
> spin_lock_irq(&conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> /* fail all writes first */
> bi = sh->dev[i].towrite;
> sh->dev[i].towrite = NULL;
> @@ -2488,6 +2500,7 @@ handle_failed_stripe(struct r5conf *conf
> bi = nextbi;
> }
> }
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
> if (bitmap_end)
> bitmap_endwrite(conf->mddev->bitmap, sh->sector,
> @@ -2695,6 +2708,7 @@ static void handle_stripe_clean_event(st
> int bitmap_end = 0;
> pr_debug("Return write for disc %d\n", i);
> spin_lock_irq(&conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> wbi = dev->written;
> dev->written = NULL;
> while (wbi && wbi->bi_sector <
> @@ -2709,6 +2723,7 @@ static void handle_stripe_clean_event(st
> }
> if (dev->towrite == NULL)
> bitmap_end = 1;
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
> if (bitmap_end)
> bitmap_endwrite(conf->mddev->bitmap,
> @@ -3168,6 +3183,7 @@ static void analyse_stripe(struct stripe
> /* Now to look around and see what can be done */
> rcu_read_lock();
> spin_lock_irq(&conf->device_lock);
> + spin_lock_irq(&sh->stripe_lock);
> for (i=disks; i--; ) {
> struct md_rdev *rdev;
> sector_t first_bad;
> @@ -3313,6 +3329,7 @@ static void analyse_stripe(struct stripe
> do_recovery = 1;
> }
> }
> + spin_unlock_irq(&sh->stripe_lock);
> spin_unlock_irq(&conf->device_lock);
> if (test_bit(STRIPE_SYNCING, &sh->state)) {
> /* If there is a failed device being replaced,
> Index: linux/drivers/md/raid5.h
> ===================================================================
> --- linux.orig/drivers/md/raid5.h 2012-06-01 13:38:54.717210079 +0800
> +++ linux/drivers/md/raid5.h 2012-06-01 13:44:19.229127709 +0800
> @@ -210,6 +210,7 @@ struct stripe_head {
> int disks; /* disks in stripe */
> enum check_states check_state;
> enum reconstruct_states reconstruct_state;
> + spinlock_t stripe_lock;
> /**
> * struct stripe_operations
> * @target - STRIPE_OP_COMPUTE_BLK target
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