netdev - Re: [RFC v3 11/11] vduse: Introduce a workqueue for irq injection

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Date:   Tue, 26 Jan 2021 16:17:28 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xie Yongji <xieyongji@...edance.com>, mst@...hat.com,
        stefanha@...hat.com, sgarzare@...hat.com, parav@...dia.com,
        bob.liu@...cle.com, hch@...radead.org, rdunlap@...radead.org,
        willy@...radead.org, viro@...iv.linux.org.uk, axboe@...nel.dk,
        bcrl@...ck.org, corbet@....net
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [RFC v3 11/11] vduse: Introduce a workqueue for irq injection


On 2021/1/19 下午1:07, Xie Yongji wrote:
> This patch introduces a dedicated workqueue for irq injection
> so that we are able to do some performance tuning for it.
>
> Signed-off-by: Xie Yongji <xieyongji@...edance.com>


If we want the split like this.

It might be better to:

1) implement a simple irq injection on the ioctl context in patch 8
2) add the dedicated workqueue injection in this patch

Since my understanding is that

1) the function looks more isolated for readers
2) the difference between sysctl vs workqueue should be more obvious 
than system wq vs dedicated wq
3) a chance to describe why workqueue is needed in the commit log in 
this patch

Thanks


> ---
>   drivers/vdpa/vdpa_user/eventfd.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa_user/eventfd.c b/drivers/vdpa/vdpa_user/eventfd.c
> index dbffddb08908..caf7d8d68ac0 100644
> --- a/drivers/vdpa/vdpa_user/eventfd.c
> +++ b/drivers/vdpa/vdpa_user/eventfd.c
> @@ -18,6 +18,7 @@
>   #include "eventfd.h"
>   
>   static struct workqueue_struct *vduse_irqfd_cleanup_wq;
> +static struct workqueue_struct *vduse_irq_wq;
>   
>   static void vduse_virqfd_shutdown(struct work_struct *work)
>   {
> @@ -57,7 +58,7 @@ static int vduse_virqfd_wakeup(wait_queue_entry_t *wait, unsigned int mode,
>   	__poll_t flags = key_to_poll(key);
>   
>   	if (flags & EPOLLIN)
> -		schedule_work(&virqfd->inject);
> +		queue_work(vduse_irq_wq, &virqfd->inject);
>   
>   	if (flags & EPOLLHUP) {
>   		spin_lock(&vq->irq_lock);
> @@ -165,11 +166,18 @@ int vduse_virqfd_init(void)
>   	if (!vduse_irqfd_cleanup_wq)
>   		return -ENOMEM;
>   
> +	vduse_irq_wq = alloc_workqueue("vduse-irq", WQ_SYSFS | WQ_UNBOUND, 0);
> +	if (!vduse_irq_wq) {
> +		destroy_workqueue(vduse_irqfd_cleanup_wq);
> +		return -ENOMEM;
> +	}
> +
>   	return 0;
>   }
>   
>   void vduse_virqfd_exit(void)
>   {
> +	destroy_workqueue(vduse_irq_wq);
>   	destroy_workqueue(vduse_irqfd_cleanup_wq);
>   }
>