[PATCH] padata: add helper function for queue length

[PATCH] padata: add helper function for queue length

[Jason A. Donenfeld]

Since padata has a maximum number of inflight jobs, currently 1000, it's
very useful to know how many jobs are currently queued up. This adds a
simple helper function to expose this information.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 include/linux/padata.h |  2 ++
 kernel/padata.c        | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/padata.h b/include/linux/padata.h
index 113ee62..4840ae4 100644
--- a/include/linux/padata.h
+++ b/include/linux/padata.h
@@ -3,6 +3,7 @@
  *
  * Copyright (C) 2008, 2009 secunet Security Networks AG
  * Copyright (C) 2008, 2009 Steffen Klassert <steffen.klassert@secunet.com>
+ * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -181,4 +182,5 @@ extern int padata_register_cpumask_notifier(struct padata_instance *pinst,
 					    struct notifier_block *nblock);
 extern int padata_unregister_cpumask_notifier(struct padata_instance *pinst,
 					      struct notifier_block *nblock);
+extern int padata_queue_len(struct padata_instance *pinst);
 #endif
diff --git a/kernel/padata.c b/kernel/padata.c
index 9932788..17c1e08 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -5,6 +5,7 @@
  *
  * Copyright (C) 2008, 2009 secunet Security Networks AG
  * Copyright (C) 2008, 2009 Steffen Klassert <steffen.klassert@secunet.com>
+ * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -1039,3 +1040,18 @@ void padata_free(struct padata_instance *pinst)
 	kobject_put(&pinst->kobj);
 }
 EXPORT_SYMBOL(padata_free);
+
+/**
+ * padata_queue_len - retreive the number of in progress jobs
+ *
+ * @padata_inst: padata instance from which to read the queue size
+ */
+int padata_queue_len(struct padata_instance *pinst)
+{
+	int len;
+	rcu_read_lock_bh();
+	len = atomic_read(&rcu_dereference_bh(pinst->pd)->refcnt);
+	rcu_read_unlock_bh();
+	return len;
+}
+EXPORT_SYMBOL(padata_queue_len);
-- 
2.10.0

Re: [PATCH] padata: add helper function for queue length

[Steffen Klassert]

On Sun, Oct 02, 2016 at 03:46:38AM +0200, Jason A. Donenfeld wrote:
> Since padata has a maximum number of inflight jobs, currently 1000, it's
> very useful to know how many jobs are currently queued up. This adds a
> simple helper function to expose this information.
> 
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  include/linux/padata.h |  2 ++
>  kernel/padata.c        | 16 ++++++++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/include/linux/padata.h b/include/linux/padata.h
> index 113ee62..4840ae4 100644
> --- a/include/linux/padata.h
> +++ b/include/linux/padata.h
> @@ -3,6 +3,7 @@
>   *
>   * Copyright (C) 2008, 2009 secunet Security Networks AG
>   * Copyright (C) 2008, 2009 Steffen Klassert <steffen.klassert@secunet.com>
> + * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>
>   *
>   * This program is free software; you can redistribute it and/or modify it
>   * under the terms and conditions of the GNU General Public License,
> @@ -181,4 +182,5 @@ extern int padata_register_cpumask_notifier(struct padata_instance *pinst,
>  					    struct notifier_block *nblock);
>  extern int padata_unregister_cpumask_notifier(struct padata_instance *pinst,
>  					      struct notifier_block *nblock);
> +extern int padata_queue_len(struct padata_instance *pinst);
>  #endif
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 9932788..17c1e08 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -5,6 +5,7 @@
>   *
>   * Copyright (C) 2008, 2009 secunet Security Networks AG
>   * Copyright (C) 2008, 2009 Steffen Klassert <steffen.klassert@secunet.com>
> + * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>
>   *
>   * This program is free software; you can redistribute it and/or modify it
>   * under the terms and conditions of the GNU General Public License,
> @@ -1039,3 +1040,18 @@ void padata_free(struct padata_instance *pinst)
>  	kobject_put(&pinst->kobj);
>  }
>  EXPORT_SYMBOL(padata_free);
> +
> +/**
> + * padata_queue_len - retreive the number of in progress jobs
> + *
> + * @padata_inst: padata instance from which to read the queue size
> + */
> +int padata_queue_len(struct padata_instance *pinst)
> +{
> +	int len;
> +	rcu_read_lock_bh();
> +	len = atomic_read(&rcu_dereference_bh(pinst->pd)->refcnt);
> +	rcu_read_unlock_bh();
> +	return len;
> +}
> +EXPORT_SYMBOL(padata_queue_len);

Why you want to have this? Without having a user of this function,
there is no point on adding it.

Re: [PATCH] padata: add helper function for queue length

[Jason A. Donenfeld]

Hi Steffen,

On Fri, Oct 7, 2016 at 5:15 AM, Steffen Klassert
<steffen.klassert@secunet.com> wrote:
> Why you want to have this?

I'm working on some bufferbloat/queue code that could benefit from
knowing how many items are currently in flight. The goal is to always
keep padata busy, but never with more jobs than absolutely necessary.
The model is CoDel.

Regards,
Jason