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Subject: Re: [PATCH 1/2] workqueue: don't always set __WQ_ORDERED implicitly
To:     linux-kernel@vger.kernel.org
Cc:     tj@kernel.org, martin.petersen@oracle.com,
        linux-scsi@vger.kernel.org, open-iscsi@googlegroups.com,
        lduncan@suse.com, michael.christie@oracle.com
References: <20200611100717.27506-1-bob.liu@oracle.com>
From:   Bob Liu <bob.liu@oracle.com>
Message-ID: <f926e5b0-b876-3dad-c1b2-33c250205452@oracle.com>
Date:   Mon, 22 Jun 2020 11:08:24 +0800
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ping..

On 6/11/20 6:07 PM, Bob Liu 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.
> 
> 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@oracle.com>
> ---
>  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))
>  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)
>