On Thu, Jun 11, 2020 at 6:29 PM Bob Liu <bob.liu@xxxxxxxxxx> wrote:
>
> Current code always set 'Unbound && max_active == 1' workqueues to ordered
> implicitly, while this may be not an expected behaviour for some use cases.
>
> E.g some scsi and iscsi workqueues(unbound && max_active = 1) want to be bind
> to different cpu so as to get better isolation, but their cpumask can't be
> changed because WQ_ORDERED is set implicitly.
Hello
If I read the code correctly, the reason why their cpumask can't
be changed is because __WQ_ORDERED_EXPLICIT, not __WQ_ORDERED.
>
> This patch adds a flag __WQ_ORDERED_DISABLE and also
> create_singlethread_workqueue_noorder() to offer an new option.
>
> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
> ---
> include/linux/workqueue.h | 4 ++++
> kernel/workqueue.c | 4 +++-
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index e48554e..4c86913 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -344,6 +344,7 @@ enum {
> __WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
> __WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */
> __WQ_ORDERED_EXPLICIT = 1 << 19, /* internal: alloc_ordered_workqueue() */
> + __WQ_ORDERED_DISABLE = 1 << 20, /* internal: don't set __WQ_ORDERED implicitly */
>
> WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
> WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
> @@ -433,6 +434,9 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
> #define create_singlethread_workqueue(name) \
> alloc_ordered_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, name)
>
> +#define create_singlethread_workqueue_noorder(name) \
> + alloc_workqueue("%s", WQ_SYSFS | __WQ_LEGACY | WQ_MEM_RECLAIM | \
> + WQ_UNBOUND | __WQ_ORDERED_DISABLE, 1, (name))
I think using __WQ_ORDERED without __WQ_ORDERED_EXPLICIT is what you
need, in which case cpumask is allowed to be changed.
Just use alloc_workqueue() with __WQ_ORDERED and max_active=1. It can
be wrapped as a new function or macro, but I don't think
create_singlethread_workqueue_noorder() is a good name for it.
> extern void destroy_workqueue(struct workqueue_struct *wq);
>
> struct workqueue_attrs *alloc_workqueue_attrs(void);
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 4e01c44..2167013 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4237,7 +4237,9 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
> * on NUMA.
> */
> if ((flags & WQ_UNBOUND) && max_active == 1)
> - flags |= __WQ_ORDERED;
> + /* the caller may don't want __WQ_ORDERED to be set implicitly. */
> + if (!(flags & __WQ_ORDERED_DISABLE))
> + flags |= __WQ_ORDERED;
>
> /* see the comment above the definition of WQ_POWER_EFFICIENT */
> if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
> --
> 2.9.5
>
