[PATCH 0/2] md: Change active_io to percpu

[PATCH 0/2] md: Change active_io to percpu

[Xiao Ni]

Hi all

This is a optimization for active_io. Now it's atomic type and
added/decreased when io comes, but it's only needed to be checked
when suspending raid. So we can change it to percpu type.

The first patch factors out a helper function which is used in
the second patch.

The patches have been tested by regression test under tests directory.
I did a performance test too. In my environment there is no big change.

Xiao Ni (2):
  Factor out is_md_suspended helper
  Change active_io to percpu

 drivers/md/md.c | 46 ++++++++++++++++++++++++++++++----------------
 drivers/md/md.h |  2 +-
 2 files changed, 31 insertions(+), 17 deletions(-)

-- 
2.32.0 (Apple Git-132)

[PATCH 1/2] md: Factor out is_md_suspended helper

[Xiao Ni]

This helper function will be used in next patch. It's easy for
understanding.

Signed-off-by: Xiao Ni <xni@redhat.com>
---
 drivers/md/md.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 775f1dde190a..d3627aad981a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -380,6 +380,13 @@ EXPORT_SYMBOL_GPL(md_new_event);
 static LIST_HEAD(all_mddevs);
 static DEFINE_SPINLOCK(all_mddevs_lock);
 
+static bool is_md_suspended(struct mddev *mddev)
+{
+	if (mddev->suspended)
+		return true;
+	else
+		return false;
+}
 /* Rather than calling directly into the personality make_request function,
  * IO requests come here first so that we can check if the device is
  * being suspended pending a reconfiguration.
@@ -389,7 +396,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
  */
 static bool is_suspended(struct mddev *mddev, struct bio *bio)
 {
-	if (mddev->suspended)
+	if (is_md_suspended(mddev))
 		return true;
 	if (bio_data_dir(bio) != WRITE)
 		return false;
@@ -434,7 +441,7 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
 		goto check_suspended;
 	}
 
-	if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
+	if (atomic_dec_and_test(&mddev->active_io) && is_md_suspended(mddev))
 		wake_up(&mddev->sb_wait);
 }
 EXPORT_SYMBOL(md_handle_request);
@@ -6217,7 +6224,7 @@ EXPORT_SYMBOL_GPL(md_stop_writes);
 static void mddev_detach(struct mddev *mddev)
 {
 	md_bitmap_wait_behind_writes(mddev);
-	if (mddev->pers && mddev->pers->quiesce && !mddev->suspended) {
+	if (mddev->pers && mddev->pers->quiesce && !is_md_suspended(mddev)) {
 		mddev->pers->quiesce(mddev, 1);
 		mddev->pers->quiesce(mddev, 0);
 	}
@@ -8529,7 +8536,7 @@ bool md_write_start(struct mddev *mddev, struct bio *bi)
 		return true;
 	wait_event(mddev->sb_wait,
 		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) ||
-		   mddev->suspended);
+		   is_md_suspended(mddev));
 	if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
 		percpu_ref_put(&mddev->writes_pending);
 		return false;
@@ -9257,7 +9264,7 @@ void md_check_recovery(struct mddev *mddev)
 		wake_up(&mddev->sb_wait);
 	}
 
-	if (mddev->suspended)
+	if (is_md_suspended(mddev))
 		return;
 
 	if (mddev->bitmap)
-- 
2.32.0 (Apple Git-132)

[PATCH 2/2] md: Change active_io to percpu

[Xiao Ni]

Now the type of active_io is atomic. It's used to count how many ios are
in the submitting process and it's added and decreased very time. But it
only needs to check if it's zero when suspending the raid. So we can
switch atomic to percpu to improve the performance.

After switching active_io to percpu type, we use the state of active_io
to judge if the raid device is suspended. And we don't need to wake up
->sb_wait in md_handle_request anymore. It's done in the callback function
which is registered when initing active_io. The argument mddev->suspended
is only used to count how many users are trying to set raid to suspend
state.

Signed-off-by: Xiao Ni <xni@redhat.com>
---
 drivers/md/md.c | 40 ++++++++++++++++++++++++----------------
 drivers/md/md.h |  2 +-
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index d3627aad981a..04c067cf2f53 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -382,10 +382,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
 
 static bool is_md_suspended(struct mddev *mddev)
 {
-	if (mddev->suspended)
-		return true;
-	else
-		return false;
+	return percpu_ref_is_dying(&mddev->active_io);
 }
 /* Rather than calling directly into the personality make_request function,
  * IO requests come here first so that we can check if the device is
@@ -412,7 +409,6 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
 void md_handle_request(struct mddev *mddev, struct bio *bio)
 {
 check_suspended:
-	rcu_read_lock();
 	if (is_suspended(mddev, bio)) {
 		DEFINE_WAIT(__wait);
 		/* Bail out if REQ_NOWAIT is set for the bio */
@@ -432,17 +428,15 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
 		}
 		finish_wait(&mddev->sb_wait, &__wait);
 	}
-	atomic_inc(&mddev->active_io);
-	rcu_read_unlock();
+	if (!percpu_ref_tryget_live(&mddev->active_io))
+		goto check_suspended;
 
 	if (!mddev->pers->make_request(mddev, bio)) {
-		atomic_dec(&mddev->active_io);
-		wake_up(&mddev->sb_wait);
+		percpu_ref_put(&mddev->active_io);
 		goto check_suspended;
 	}
 
-	if (atomic_dec_and_test(&mddev->active_io) && is_md_suspended(mddev))
-		wake_up(&mddev->sb_wait);
+	percpu_ref_put(&mddev->active_io);
 }
 EXPORT_SYMBOL(md_handle_request);
 
@@ -488,11 +482,10 @@ void mddev_suspend(struct mddev *mddev)
 	lockdep_assert_held(&mddev->reconfig_mutex);
 	if (mddev->suspended++)
 		return;
-	synchronize_rcu();
 	wake_up(&mddev->sb_wait);
 	set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags);
-	smp_mb__after_atomic();
-	wait_event(mddev->sb_wait, atomic_read(&mddev->active_io) == 0);
+	percpu_ref_kill(&mddev->active_io);
+	wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
 	mddev->pers->quiesce(mddev, 1);
 	clear_bit_unlock(MD_ALLOW_SB_UPDATE, &mddev->flags);
 	wait_event(mddev->sb_wait, !test_bit(MD_UPDATING_SB, &mddev->flags));
@@ -510,6 +503,7 @@ void mddev_resume(struct mddev *mddev)
 	lockdep_assert_held(&mddev->reconfig_mutex);
 	if (--mddev->suspended)
 		return;
+	percpu_ref_resurrect(&mddev->active_io);
 	wake_up(&mddev->sb_wait);
 	mddev->pers->quiesce(mddev, 0);
 
@@ -688,7 +682,6 @@ void mddev_init(struct mddev *mddev)
 	timer_setup(&mddev->safemode_timer, md_safemode_timeout, 0);
 	atomic_set(&mddev->active, 1);
 	atomic_set(&mddev->openers, 0);
-	atomic_set(&mddev->active_io, 0);
 	spin_lock_init(&mddev->lock);
 	atomic_set(&mddev->flush_pending, 0);
 	init_waitqueue_head(&mddev->sb_wait);
@@ -5765,6 +5758,12 @@ static void md_safemode_timeout(struct timer_list *t)
 }
 
 static int start_dirty_degraded;
+static void active_io_release(struct percpu_ref *ref)
+{
+	struct mddev *mddev = container_of(ref, struct mddev, active_io);
+
+	wake_up(&mddev->sb_wait);
+}
 
 int md_run(struct mddev *mddev)
 {
@@ -5845,10 +5844,15 @@ int md_run(struct mddev *mddev)
 		nowait = nowait && bdev_nowait(rdev->bdev);
 	}
 
+	err = percpu_ref_init(&mddev->active_io, active_io_release,
+				PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
+	if (err)
+		return err;
+
 	if (!bioset_initialized(&mddev->bio_set)) {
 		err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
 		if (err)
-			return err;
+			goto exit_active_io;
 	}
 	if (!bioset_initialized(&mddev->sync_set)) {
 		err = bioset_init(&mddev->sync_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
@@ -6036,6 +6040,8 @@ int md_run(struct mddev *mddev)
 	bioset_exit(&mddev->sync_set);
 exit_bio_set:
 	bioset_exit(&mddev->bio_set);
+exit_active_io:
+	percpu_ref_exit(&mddev->active_io);
 	return err;
 }
 EXPORT_SYMBOL_GPL(md_run);
@@ -6260,6 +6266,7 @@ void md_stop(struct mddev *mddev)
 	 */
 	__md_stop_writes(mddev);
 	__md_stop(mddev);
+	percpu_ref_exit(&mddev->active_io);
 	bioset_exit(&mddev->bio_set);
 	bioset_exit(&mddev->sync_set);
 }
@@ -7833,6 +7840,7 @@ static void md_free_disk(struct gendisk *disk)
 	struct mddev *mddev = disk->private_data;
 
 	percpu_ref_exit(&mddev->writes_pending);
+	percpu_ref_exit(&mddev->active_io);
 	bioset_exit(&mddev->bio_set);
 	bioset_exit(&mddev->sync_set);
 
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 554a9026669a..6335cb86e52e 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -315,7 +315,7 @@ struct mddev {
 	unsigned long			sb_flags;
 
 	int				suspended;
-	atomic_t			active_io;
+	struct percpu_ref		active_io;
 	int				ro;
 	int				sysfs_active; /* set when sysfs deletes
 						       * are happening, so run/
-- 
2.32.0 (Apple Git-132)

Re: [PATCH 1/2] md: Factor out is_md_suspended helper

[Paul Menzel]

Dear Xiao,


Thank you for the patch.

Am 21.01.23 um 02:39 schrieb Xiao Ni:
> This helper function will be used in next patch. It's easy for
> understanding.
> 
> Signed-off-by: Xiao Ni <xni@redhat.com>
> ---
>   drivers/md/md.c | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 775f1dde190a..d3627aad981a 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -380,6 +380,13 @@ EXPORT_SYMBOL_GPL(md_new_event);
>   static LIST_HEAD(all_mddevs);
>   static DEFINE_SPINLOCK(all_mddevs_lock);
>   
> +static bool is_md_suspended(struct mddev *mddev)
> +{
> +	if (mddev->suspended)
> +		return true;
> +	else
> +		return false;

suspended seems to be an integer, so this could be written as:

     return !!mddev->suspended;

or

     return (mddev->suspended) ? true : false;


Kind regards,

Paul


> +}
>   /* Rather than calling directly into the personality make_request function,
>    * IO requests come here first so that we can check if the device is
>    * being suspended pending a reconfiguration.
> @@ -389,7 +396,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
>    */
>   static bool is_suspended(struct mddev *mddev, struct bio *bio)
>   {
> -	if (mddev->suspended)
> +	if (is_md_suspended(mddev))
>   		return true;
>   	if (bio_data_dir(bio) != WRITE)
>   		return false;
> @@ -434,7 +441,7 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
>   		goto check_suspended;
>   	}
>   
> -	if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
> +	if (atomic_dec_and_test(&mddev->active_io) && is_md_suspended(mddev))
>   		wake_up(&mddev->sb_wait);
>   }
>   EXPORT_SYMBOL(md_handle_request);
> @@ -6217,7 +6224,7 @@ EXPORT_SYMBOL_GPL(md_stop_writes);
>   static void mddev_detach(struct mddev *mddev)
>   {
>   	md_bitmap_wait_behind_writes(mddev);
> -	if (mddev->pers && mddev->pers->quiesce && !mddev->suspended) {
> +	if (mddev->pers && mddev->pers->quiesce && !is_md_suspended(mddev)) {
>   		mddev->pers->quiesce(mddev, 1);
>   		mddev->pers->quiesce(mddev, 0);
>   	}
> @@ -8529,7 +8536,7 @@ bool md_write_start(struct mddev *mddev, struct bio *bi)
>   		return true;
>   	wait_event(mddev->sb_wait,
>   		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) ||
> -		   mddev->suspended);
> +		   is_md_suspended(mddev));
>   	if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
>   		percpu_ref_put(&mddev->writes_pending);
>   		return false;
> @@ -9257,7 +9264,7 @@ void md_check_recovery(struct mddev *mddev)
>   		wake_up(&mddev->sb_wait);
>   	}
>   
> -	if (mddev->suspended)
> +	if (is_md_suspended(mddev))
>   		return;
>   
>   	if (mddev->bitmap)

Re: [PATCH 2/2] md: Change active_io to percpu

[Paul Menzel]

Dear Xiao,


Am 21.01.23 um 02:39 schrieb Xiao Ni:
> Now the type of active_io is atomic. It's used to count how many ios are
> in the submitting process and it's added and decreased very time. But it

s/very/every/

> only needs to check if it's zero when suspending the raid. So we can
> switch atomic to percpu to improve the performance.
> 
> After switching active_io to percpu type, we use the state of active_io
> to judge if the raid device is suspended. And we don't need to wake up
> ->sb_wait in md_handle_request anymore. It's done in the callback function
> which is registered when initing active_io. The argument mddev->suspended
> is only used to count how many users are trying to set raid to suspend
> state.

How did you measure the performance impact?


Kind regards,

Paul


> Signed-off-by: Xiao Ni <xni@redhat.com>
> ---
>   drivers/md/md.c | 40 ++++++++++++++++++++++++----------------
>   drivers/md/md.h |  2 +-
>   2 files changed, 25 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index d3627aad981a..04c067cf2f53 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -382,10 +382,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
>   
>   static bool is_md_suspended(struct mddev *mddev)
>   {
> -	if (mddev->suspended)
> -		return true;
> -	else
> -		return false;
> +	return percpu_ref_is_dying(&mddev->active_io);
>   }
>   /* Rather than calling directly into the personality make_request function,
>    * IO requests come here first so that we can check if the device is
> @@ -412,7 +409,6 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
>   void md_handle_request(struct mddev *mddev, struct bio *bio)
>   {
>   check_suspended:
> -	rcu_read_lock();
>   	if (is_suspended(mddev, bio)) {
>   		DEFINE_WAIT(__wait);
>   		/* Bail out if REQ_NOWAIT is set for the bio */
> @@ -432,17 +428,15 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
>   		}
>   		finish_wait(&mddev->sb_wait, &__wait);
>   	}
> -	atomic_inc(&mddev->active_io);
> -	rcu_read_unlock();
> +	if (!percpu_ref_tryget_live(&mddev->active_io))
> +		goto check_suspended;
>   
>   	if (!mddev->pers->make_request(mddev, bio)) {
> -		atomic_dec(&mddev->active_io);
> -		wake_up(&mddev->sb_wait);
> +		percpu_ref_put(&mddev->active_io);
>   		goto check_suspended;
>   	}
>   
> -	if (atomic_dec_and_test(&mddev->active_io) && is_md_suspended(mddev))
> -		wake_up(&mddev->sb_wait);
> +	percpu_ref_put(&mddev->active_io);
>   }
>   EXPORT_SYMBOL(md_handle_request);
>   
> @@ -488,11 +482,10 @@ void mddev_suspend(struct mddev *mddev)
>   	lockdep_assert_held(&mddev->reconfig_mutex);
>   	if (mddev->suspended++)
>   		return;
> -	synchronize_rcu();
>   	wake_up(&mddev->sb_wait);
>   	set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags);
> -	smp_mb__after_atomic();
> -	wait_event(mddev->sb_wait, atomic_read(&mddev->active_io) == 0);
> +	percpu_ref_kill(&mddev->active_io);
> +	wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
>   	mddev->pers->quiesce(mddev, 1);
>   	clear_bit_unlock(MD_ALLOW_SB_UPDATE, &mddev->flags);
>   	wait_event(mddev->sb_wait, !test_bit(MD_UPDATING_SB, &mddev->flags));
> @@ -510,6 +503,7 @@ void mddev_resume(struct mddev *mddev)
>   	lockdep_assert_held(&mddev->reconfig_mutex);
>   	if (--mddev->suspended)
>   		return;
> +	percpu_ref_resurrect(&mddev->active_io);
>   	wake_up(&mddev->sb_wait);
>   	mddev->pers->quiesce(mddev, 0);
>   
> @@ -688,7 +682,6 @@ void mddev_init(struct mddev *mddev)
>   	timer_setup(&mddev->safemode_timer, md_safemode_timeout, 0);
>   	atomic_set(&mddev->active, 1);
>   	atomic_set(&mddev->openers, 0);
> -	atomic_set(&mddev->active_io, 0);
>   	spin_lock_init(&mddev->lock);
>   	atomic_set(&mddev->flush_pending, 0);
>   	init_waitqueue_head(&mddev->sb_wait);
> @@ -5765,6 +5758,12 @@ static void md_safemode_timeout(struct timer_list *t)
>   }
>   
>   static int start_dirty_degraded;
> +static void active_io_release(struct percpu_ref *ref)
> +{
> +	struct mddev *mddev = container_of(ref, struct mddev, active_io);
> +
> +	wake_up(&mddev->sb_wait);
> +}
>   
>   int md_run(struct mddev *mddev)
>   {
> @@ -5845,10 +5844,15 @@ int md_run(struct mddev *mddev)
>   		nowait = nowait && bdev_nowait(rdev->bdev);
>   	}
>   
> +	err = percpu_ref_init(&mddev->active_io, active_io_release,
> +				PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
> +	if (err)
> +		return err;
> +
>   	if (!bioset_initialized(&mddev->bio_set)) {
>   		err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
>   		if (err)
> -			return err;
> +			goto exit_active_io;
>   	}
>   	if (!bioset_initialized(&mddev->sync_set)) {
>   		err = bioset_init(&mddev->sync_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
> @@ -6036,6 +6040,8 @@ int md_run(struct mddev *mddev)
>   	bioset_exit(&mddev->sync_set);
>   exit_bio_set:
>   	bioset_exit(&mddev->bio_set);
> +exit_active_io:
> +	percpu_ref_exit(&mddev->active_io);
>   	return err;
>   }
>   EXPORT_SYMBOL_GPL(md_run);
> @@ -6260,6 +6266,7 @@ void md_stop(struct mddev *mddev)
>   	 */
>   	__md_stop_writes(mddev);
>   	__md_stop(mddev);
> +	percpu_ref_exit(&mddev->active_io);
>   	bioset_exit(&mddev->bio_set);
>   	bioset_exit(&mddev->sync_set);
>   }
> @@ -7833,6 +7840,7 @@ static void md_free_disk(struct gendisk *disk)
>   	struct mddev *mddev = disk->private_data;
>   
>   	percpu_ref_exit(&mddev->writes_pending);
> +	percpu_ref_exit(&mddev->active_io);
>   	bioset_exit(&mddev->bio_set);
>   	bioset_exit(&mddev->sync_set);
>   
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 554a9026669a..6335cb86e52e 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -315,7 +315,7 @@ struct mddev {
>   	unsigned long			sb_flags;
>   
>   	int				suspended;
> -	atomic_t			active_io;
> +	struct percpu_ref		active_io;
>   	int				ro;
>   	int				sysfs_active; /* set when sysfs deletes
>   						       * are happening, so run/

Re: [PATCH 1/2] md: Factor out is_md_suspended helper

[Xiao Ni]

On Mon, Jan 23, 2023 at 9:18 PM Paul Menzel <pmenzel@molgen.mpg.de> wrote:
>
> Dear Xiao,
>
>
> Thank you for the patch.
>
> Am 21.01.23 um 02:39 schrieb Xiao Ni:
> > This helper function will be used in next patch. It's easy for
> > understanding.
> >
> > Signed-off-by: Xiao Ni <xni@redhat.com>
> > ---
> >   drivers/md/md.c | 17 ++++++++++++-----
> >   1 file changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 775f1dde190a..d3627aad981a 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -380,6 +380,13 @@ EXPORT_SYMBOL_GPL(md_new_event);
> >   static LIST_HEAD(all_mddevs);
> >   static DEFINE_SPINLOCK(all_mddevs_lock);
> >
> > +static bool is_md_suspended(struct mddev *mddev)
> > +{
> > +     if (mddev->suspended)
> > +             return true;
> > +     else
> > +             return false;
>
> suspended seems to be an integer, so this could be written as:
>
>      return !!mddev->suspended;
>
> or
>
>      return (mddev->suspended) ? true : false;
>
>
> Kind regards,
>
> Paul

Hi Paul

Thanks for this.

Regards
Xiao
>
>
> > +}
> >   /* Rather than calling directly into the personality make_request function,
> >    * IO requests come here first so that we can check if the device is
> >    * being suspended pending a reconfiguration.
> > @@ -389,7 +396,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
> >    */
> >   static bool is_suspended(struct mddev *mddev, struct bio *bio)
> >   {
> > -     if (mddev->suspended)
> > +     if (is_md_suspended(mddev))
> >               return true;
> >       if (bio_data_dir(bio) != WRITE)
> >               return false;
> > @@ -434,7 +441,7 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
> >               goto check_suspended;
> >       }
> >
> > -     if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
> > +     if (atomic_dec_and_test(&mddev->active_io) && is_md_suspended(mddev))
> >               wake_up(&mddev->sb_wait);
> >   }
> >   EXPORT_SYMBOL(md_handle_request);
> > @@ -6217,7 +6224,7 @@ EXPORT_SYMBOL_GPL(md_stop_writes);
> >   static void mddev_detach(struct mddev *mddev)
> >   {
> >       md_bitmap_wait_behind_writes(mddev);
> > -     if (mddev->pers && mddev->pers->quiesce && !mddev->suspended) {
> > +     if (mddev->pers && mddev->pers->quiesce && !is_md_suspended(mddev)) {
> >               mddev->pers->quiesce(mddev, 1);
> >               mddev->pers->quiesce(mddev, 0);
> >       }
> > @@ -8529,7 +8536,7 @@ bool md_write_start(struct mddev *mddev, struct bio *bi)
> >               return true;
> >       wait_event(mddev->sb_wait,
> >                  !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) ||
> > -                mddev->suspended);
> > +                is_md_suspended(mddev));
> >       if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
> >               percpu_ref_put(&mddev->writes_pending);
> >               return false;
> > @@ -9257,7 +9264,7 @@ void md_check_recovery(struct mddev *mddev)
> >               wake_up(&mddev->sb_wait);
> >       }
> >
> > -     if (mddev->suspended)
> > +     if (is_md_suspended(mddev))
> >               return;
> >
> >       if (mddev->bitmap)
>

Re: [PATCH 2/2] md: Change active_io to percpu

[Xiao Ni]

On Mon, Jan 23, 2023 at 9:22 PM Paul Menzel <pmenzel@molgen.mpg.de> wrote:
>
> Dear Xiao,
>
>
> Am 21.01.23 um 02:39 schrieb Xiao Ni:
> > Now the type of active_io is atomic. It's used to count how many ios are
> > in the submitting process and it's added and decreased very time. But it
>
> s/very/every/
>
> > only needs to check if it's zero when suspending the raid. So we can
> > switch atomic to percpu to improve the performance.
> >
> > After switching active_io to percpu type, we use the state of active_io
> > to judge if the raid device is suspended. And we don't need to wake up
> > ->sb_wait in md_handle_request anymore. It's done in the callback function
> > which is registered when initing active_io. The argument mddev->suspended
> > is only used to count how many users are trying to set raid to suspend
> > state.
>
> How did you measure the performance impact?

Hi Paul

I used fio to do read/write/randread/randwrite tests on a raid0(nvme ssd hdd).
In my environment, there is no big change about the results.

Best Regards
Xiao
>
>
> Kind regards,
>
> Paul
>
>
> > Signed-off-by: Xiao Ni <xni@redhat.com>
> > ---
> >   drivers/md/md.c | 40 ++++++++++++++++++++++++----------------
> >   drivers/md/md.h |  2 +-
> >   2 files changed, 25 insertions(+), 17 deletions(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index d3627aad981a..04c067cf2f53 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -382,10 +382,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
> >
> >   static bool is_md_suspended(struct mddev *mddev)
> >   {
> > -     if (mddev->suspended)
> > -             return true;
> > -     else
> > -             return false;
> > +     return percpu_ref_is_dying(&mddev->active_io);
> >   }
> >   /* Rather than calling directly into the personality make_request function,
> >    * IO requests come here first so that we can check if the device is
> > @@ -412,7 +409,6 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
> >   void md_handle_request(struct mddev *mddev, struct bio *bio)
> >   {
> >   check_suspended:
> > -     rcu_read_lock();
> >       if (is_suspended(mddev, bio)) {
> >               DEFINE_WAIT(__wait);
> >               /* Bail out if REQ_NOWAIT is set for the bio */
> > @@ -432,17 +428,15 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
> >               }
> >               finish_wait(&mddev->sb_wait, &__wait);
> >       }
> > -     atomic_inc(&mddev->active_io);
> > -     rcu_read_unlock();
> > +     if (!percpu_ref_tryget_live(&mddev->active_io))
> > +             goto check_suspended;
> >
> >       if (!mddev->pers->make_request(mddev, bio)) {
> > -             atomic_dec(&mddev->active_io);
> > -             wake_up(&mddev->sb_wait);
> > +             percpu_ref_put(&mddev->active_io);
> >               goto check_suspended;
> >       }
> >
> > -     if (atomic_dec_and_test(&mddev->active_io) && is_md_suspended(mddev))
> > -             wake_up(&mddev->sb_wait);
> > +     percpu_ref_put(&mddev->active_io);
> >   }
> >   EXPORT_SYMBOL(md_handle_request);
> >
> > @@ -488,11 +482,10 @@ void mddev_suspend(struct mddev *mddev)
> >       lockdep_assert_held(&mddev->reconfig_mutex);
> >       if (mddev->suspended++)
> >               return;
> > -     synchronize_rcu();
> >       wake_up(&mddev->sb_wait);
> >       set_bit(MD_ALLOW_SB_UPDATE, &mddev->flags);
> > -     smp_mb__after_atomic();
> > -     wait_event(mddev->sb_wait, atomic_read(&mddev->active_io) == 0);
> > +     percpu_ref_kill(&mddev->active_io);
> > +     wait_event(mddev->sb_wait, percpu_ref_is_zero(&mddev->active_io));
> >       mddev->pers->quiesce(mddev, 1);
> >       clear_bit_unlock(MD_ALLOW_SB_UPDATE, &mddev->flags);
> >       wait_event(mddev->sb_wait, !test_bit(MD_UPDATING_SB, &mddev->flags));
> > @@ -510,6 +503,7 @@ void mddev_resume(struct mddev *mddev)
> >       lockdep_assert_held(&mddev->reconfig_mutex);
> >       if (--mddev->suspended)
> >               return;
> > +     percpu_ref_resurrect(&mddev->active_io);
> >       wake_up(&mddev->sb_wait);
> >       mddev->pers->quiesce(mddev, 0);
> >
> > @@ -688,7 +682,6 @@ void mddev_init(struct mddev *mddev)
> >       timer_setup(&mddev->safemode_timer, md_safemode_timeout, 0);
> >       atomic_set(&mddev->active, 1);
> >       atomic_set(&mddev->openers, 0);
> > -     atomic_set(&mddev->active_io, 0);
> >       spin_lock_init(&mddev->lock);
> >       atomic_set(&mddev->flush_pending, 0);
> >       init_waitqueue_head(&mddev->sb_wait);
> > @@ -5765,6 +5758,12 @@ static void md_safemode_timeout(struct timer_list *t)
> >   }
> >
> >   static int start_dirty_degraded;
> > +static void active_io_release(struct percpu_ref *ref)
> > +{
> > +     struct mddev *mddev = container_of(ref, struct mddev, active_io);
> > +
> > +     wake_up(&mddev->sb_wait);
> > +}
> >
> >   int md_run(struct mddev *mddev)
> >   {
> > @@ -5845,10 +5844,15 @@ int md_run(struct mddev *mddev)
> >               nowait = nowait && bdev_nowait(rdev->bdev);
> >       }
> >
> > +     err = percpu_ref_init(&mddev->active_io, active_io_release,
> > +                             PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
> > +     if (err)
> > +             return err;
> > +
> >       if (!bioset_initialized(&mddev->bio_set)) {
> >               err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
> >               if (err)
> > -                     return err;
> > +                     goto exit_active_io;
> >       }
> >       if (!bioset_initialized(&mddev->sync_set)) {
> >               err = bioset_init(&mddev->sync_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
> > @@ -6036,6 +6040,8 @@ int md_run(struct mddev *mddev)
> >       bioset_exit(&mddev->sync_set);
> >   exit_bio_set:
> >       bioset_exit(&mddev->bio_set);
> > +exit_active_io:
> > +     percpu_ref_exit(&mddev->active_io);
> >       return err;
> >   }
> >   EXPORT_SYMBOL_GPL(md_run);
> > @@ -6260,6 +6266,7 @@ void md_stop(struct mddev *mddev)
> >        */
> >       __md_stop_writes(mddev);
> >       __md_stop(mddev);
> > +     percpu_ref_exit(&mddev->active_io);
> >       bioset_exit(&mddev->bio_set);
> >       bioset_exit(&mddev->sync_set);
> >   }
> > @@ -7833,6 +7840,7 @@ static void md_free_disk(struct gendisk *disk)
> >       struct mddev *mddev = disk->private_data;
> >
> >       percpu_ref_exit(&mddev->writes_pending);
> > +     percpu_ref_exit(&mddev->active_io);
> >       bioset_exit(&mddev->bio_set);
> >       bioset_exit(&mddev->sync_set);
> >
> > diff --git a/drivers/md/md.h b/drivers/md/md.h
> > index 554a9026669a..6335cb86e52e 100644
> > --- a/drivers/md/md.h
> > +++ b/drivers/md/md.h
> > @@ -315,7 +315,7 @@ struct mddev {
> >       unsigned long                   sb_flags;
> >
> >       int                             suspended;
> > -     atomic_t                        active_io;
> > +     struct percpu_ref               active_io;
> >       int                             ro;
> >       int                             sysfs_active; /* set when sysfs deletes
> >                                                      * are happening, so run/
>

Re: [PATCH 2/2] md: Change active_io to percpu

[Ming Lei]

On Sat, Jan 21, 2023 at 09:39:37AM +0800, Xiao Ni wrote:
> Now the type of active_io is atomic. It's used to count how many ios are
> in the submitting process and it's added and decreased very time. But it
> only needs to check if it's zero when suspending the raid. So we can
> switch atomic to percpu to improve the performance.
> 
> After switching active_io to percpu type, we use the state of active_io
> to judge if the raid device is suspended. And we don't need to wake up
> ->sb_wait in md_handle_request anymore. It's done in the callback function
> which is registered when initing active_io. The argument mddev->suspended
> is only used to count how many users are trying to set raid to suspend
> state.
> 
> Signed-off-by: Xiao Ni <xni@redhat.com>
> ---
>  drivers/md/md.c | 40 ++++++++++++++++++++++++----------------
>  drivers/md/md.h |  2 +-
>  2 files changed, 25 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index d3627aad981a..04c067cf2f53 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -382,10 +382,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
>  
>  static bool is_md_suspended(struct mddev *mddev)
>  {
> -	if (mddev->suspended)
> -		return true;
> -	else
> -		return false;
> +	return percpu_ref_is_dying(&mddev->active_io);
>  }
>  /* Rather than calling directly into the personality make_request function,
>   * IO requests come here first so that we can check if the device is
> @@ -412,7 +409,6 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
>  void md_handle_request(struct mddev *mddev, struct bio *bio)
>  {
>  check_suspended:
> -	rcu_read_lock();
>  	if (is_suspended(mddev, bio)) {
>  		DEFINE_WAIT(__wait);
>  		/* Bail out if REQ_NOWAIT is set for the bio */
> @@ -432,17 +428,15 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
>  		}
>  		finish_wait(&mddev->sb_wait, &__wait);
>  	}

Hi Xiao,

All rcu_read_unlock/rcu_read_lock should be removed from the above
branch, and that could cause the ktest robot warning.

Thanks,
Ming