On Mon, 25 Jun 2012 15:24:53 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
> release_stripe() is a place conf->device_lock is heavily contended. We take the
> lock even stripe count isn't 1, which isn't required.
>
> Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
> ---
> drivers/md/raid5.c | 73 +++++++++++++++++++++++++++++------------------------
> 1 file changed, 40 insertions(+), 33 deletions(-)
>
> Index: linux/drivers/md/raid5.c
> ===================================================================
> --- linux.orig/drivers/md/raid5.c 2012-06-25 14:37:21.000000000 +0800
> +++ linux/drivers/md/raid5.c 2012-06-25 14:38:13.899130571 +0800
> @@ -196,49 +196,56 @@ static int stripe_operations_active(stru
> test_bit(STRIPE_COMPUTE_RUN, &sh->state);
> }
>
> -static void __release_stripe(struct r5conf *conf, struct stripe_head *sh)
> +static void handle_release_stripe(struct r5conf *conf, struct stripe_head *sh)
> {
> - if (atomic_dec_and_test(&sh->count)) {
> - BUG_ON(!list_empty(&sh->lru));
> - BUG_ON(atomic_read(&conf->active_stripes)==0);
> - if (test_bit(STRIPE_HANDLE, &sh->state)) {
> - if (test_bit(STRIPE_DELAYED, &sh->state) &&
> - !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> - list_add_tail(&sh->lru, &conf->delayed_list);
> - else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
> - sh->bm_seq - conf->seq_write > 0)
> - list_add_tail(&sh->lru, &conf->bitmap_list);
> - else {
> - clear_bit(STRIPE_DELAYED, &sh->state);
> - clear_bit(STRIPE_BIT_DELAY, &sh->state);
> - list_add_tail(&sh->lru, &conf->handle_list);
> - }
> - md_wakeup_thread(conf->mddev->thread);
> - } else {
> - BUG_ON(stripe_operations_active(sh));
> - if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> - if (atomic_dec_return(&conf->preread_active_stripes)
> - < IO_THRESHOLD)
> - md_wakeup_thread(conf->mddev->thread);
> - atomic_dec(&conf->active_stripes);
> - if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
> - list_add_tail(&sh->lru, &conf->inactive_list);
> - wake_up(&conf->wait_for_stripe);
> - if (conf->retry_read_aligned)
> - md_wakeup_thread(conf->mddev->thread);
> - }
> + BUG_ON(!list_empty(&sh->lru));
> + BUG_ON(atomic_read(&conf->active_stripes)==0);
> + if (test_bit(STRIPE_HANDLE, &sh->state)) {
> + if (test_bit(STRIPE_DELAYED, &sh->state) &&
> + !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> + list_add_tail(&sh->lru, &conf->delayed_list);
> + else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
> + sh->bm_seq - conf->seq_write > 0)
> + list_add_tail(&sh->lru, &conf->bitmap_list);
> + else {
> + clear_bit(STRIPE_DELAYED, &sh->state);
> + clear_bit(STRIPE_BIT_DELAY, &sh->state);
> + list_add_tail(&sh->lru, &conf->handle_list);
> + }
> + md_wakeup_thread(conf->mddev->thread);
> + } else {
> + BUG_ON(stripe_operations_active(sh));
> + if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> + if (atomic_dec_return(&conf->preread_active_stripes)
> + < IO_THRESHOLD)
> + md_wakeup_thread(conf->mddev->thread);
> + atomic_dec(&conf->active_stripes);
> + if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
> + list_add_tail(&sh->lru, &conf->inactive_list);
> + wake_up(&conf->wait_for_stripe);
> + if (conf->retry_read_aligned)
> + md_wakeup_thread(conf->mddev->thread);
> }
> }
> }
>
> +static void __release_stripe(struct r5conf *conf, struct stripe_head *sh)
> +{
> + if (atomic_dec_and_test(&sh->count))
> + handle_release_stripe(conf, sh);
> +}
> +
> static void release_stripe(struct stripe_head *sh)
> {
> struct r5conf *conf = sh->raid_conf;
> unsigned long flags;
>
> - spin_lock_irqsave(&conf->device_lock, flags);
> - __release_stripe(conf, sh);
> - spin_unlock_irqrestore(&conf->device_lock, flags);
> + local_irq_save(flags);
> + if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
> + handle_release_stripe(conf, sh);
> + spin_unlock(&conf->device_lock);
> + }
> + local_irq_restore(flags);
> }
>
> static inline void remove_hash(struct stripe_head *sh)
Thanks. I've applied this patch and it should appear in my -next shortly.
I renamed "handle_release_stripe" to "do_release_stripe", partly because I
think that is more consistent with practice in Linux, but mostly because
"handle" means something else inside raid5.c and I don't want to encourage
confusion.
Thanks,
NeilBrown
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