Re: [PATCH wq/for-3.14 1/2] workqueue: update max_active clamping rules

Rafael J. Wysocki
2013-12-20T01:13:17Z

On Thursday, December 19, 2013 06:35:26 PM Tejun Heo wrote:
> From bdd220b2a1b86fee14a12b69fb0cadafe60a1dac Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@kernel.org>
> Date: Thu, 19 Dec 2013 18:33:09 -0500
>
> @max_active handling is currently inconsistent.
>
> * In alloc_workqueue(), 0 gets converted to the default and the value
> gets clamped to [1, lim].
>
> * In workqueue_set_max_active(), 0 is not converted to the default and
> the value is clamped to [1, lim].
>
> * When a workqueue is exposed through sysfs, input < 1 fails with
> -EINVAL; otherwise, the value is clamped to [1, lim].
>
> * fscache exposes max_active through a sysctl and clamps the value in
> [1, lim].
>
> We want to be able to express zero @max_active but as it's a special
> case and 0 is already used for default, don't want to use 0 for it.
> Update @max_active clamping so that the following rules are followed.
>
> * In both alloc_workqueue() and workqueue_set_max_active(), 0 is
> converted to the default, and a new special value WQ_FROZEN_ACTIVE
> becomes 0; otherwise, the value is clamped to [1, lim].
>
> * In both sysfs and fscache sysctl, input < 1 fails with -EINVAL;
> otherwise, the value is clamped to [1, lim].
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> Cc: David Howells <dhowells@redhat.com>

Well, this one looks good to me:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> fs/fscache/main.c | 10 +++++++---
> include/linux/workqueue.h | 1 +
> kernel/workqueue.c | 6 +++++-
> 3 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fscache/main.c b/fs/fscache/main.c
> index 7c27907..9d5a716 100644
> --- a/fs/fscache/main.c
> +++ b/fs/fscache/main.c
> @@ -62,9 +62,13 @@ static int fscache_max_active_sysctl(struct ctl_table *table, int write,
> int ret;
>
> ret = proc_dointvec(table, write, buffer, lenp, ppos);
> - if (ret == 0)
> - workqueue_set_max_active(*wqp, *datap);
> - return ret;
> + if (ret < 0)
> + return ret;
> + if (*datap < 1)
> + return -EINVAL;
> +
> + workqueue_set_max_active(*wqp, *datap);
> + return 0;
> }
>
> ctl_table fscache_sysctls[] = {
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 594521b..334daa3 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -338,6 +338,7 @@ enum {
> __WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
> __WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
>
> + WQ_FROZEN_ACTIVE = -1, /* special value for frozen wq */
> WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
> WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
> WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 987293d..6748fbf 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4136,6 +4136,11 @@ static int wq_clamp_max_active(int max_active, unsigned int flags,
> {
> int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
>
> + if (max_active == 0)
> + return WQ_DFL_ACTIVE;
> + if (max_active == WQ_FROZEN_ACTIVE)
> + return 0;
> +
> if (max_active < 1 || max_active > lim)
> pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
> max_active, name, 1, lim);
> @@ -4176,7 +4181,6 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
> vsnprintf(wq->name, sizeof(wq->name), fmt, args);
> va_end(args);
>
> - max_active = max_active ?: WQ_DFL_ACTIVE;
> max_active = wq_clamp_max_active(max_active, flags, wq->name);
>
> /* init wq */
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.