Re: [PATCH 4/4] raid5: fix wakeup condition

[NeilBrown <neilb@suse.de>]

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On Thu, 28 May 2015 17:33:48 -0700 Shaohua Li <shli@fb.com> wrote:

> Since we have several stripe hash list, the conf->active_stripes doesn't
> determine if there is free stripe in a specific hash list, so delete the
> check. After this, the R5_INACTIVE_BLOCKED check is inappropriate. There
> is no point not to wakeup a task if there is free stripe.
> 
> Signed-off-by: Shaohua Li <shli@fb.com>
> ---
>  drivers/md/raid5.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 67626f3..4b5a03c 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -687,11 +687,7 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
>  					&conf->cache_state);
>  				wait_event_lock_irq(
>  					conf->wait_for_stripe,
> -					!list_empty(conf->inactive_list + hash) &&
> -					(atomic_read(&conf->active_stripes)
> -					 < (conf->max_nr_stripes * 3 / 4)
> -					 || !test_bit(R5_INACTIVE_BLOCKED,
> -						      &conf->cache_state)),
> +					!list_empty(conf->inactive_list + hash),
>  					*(conf->hash_locks + hash));
>  				clear_bit(R5_INACTIVE_BLOCKED,
>  					  &conf->cache_state);

Have you actually tested this?  Because I do remember why I put that code in
and it made a very real performance improvement.

The idea is that once we run out of free stripes, we wait until there a lots
available.  That improves opportunities for batching.

So I would definitely needs some performance numbers with a patch like this.

Thanks for the review anyway !!

NeilBrown

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