linux-kernel - Re: [V9fs-developer] [PATCH v3] Fix a hard lockup case in the virtio transport

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Date:   Thu, 19 Jul 2018 15:48:01 +0800
From:   piaojun <piaojun@...wei.com>
To:     jiangyiwen <jiangyiwen@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        "Ron Minnich" <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>
CC:     <v9fs-developer@...ts.sourceforge.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [V9fs-developer] [PATCH v3] Fix a hard lockup case in the virtio
 transport

LGTM

On 2018/7/19 15:17, jiangyiwen wrote:
> When client has multiple threads that issue io requests
> all the time, and the server has a very good performance,
> it may cause cpu is running in the irq context for a long
> time because it can check virtqueue has buf in the *while*
> loop.
> 
> So we should keep chan->lock in the whole loop.
> 
> Signed-off-by: Yiwen Jiang <jiangyiwen@...wei.com>
Reviewed-by: Jun Piao <piaojun@...wei.com>
> ---
>  net/9p/trans_virtio.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 05006cb..3589864 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -144,24 +144,25 @@ static void req_done(struct virtqueue *vq)
>  	struct virtio_chan *chan = vq->vdev->priv;
>  	unsigned int len;
>  	struct p9_req_t *req;
> +	bool need_wakeup = false;
>  	unsigned long flags;
> 
>  	p9_debug(P9_DEBUG_TRANS, ": request done\n");
> 
> -	while (1) {
> -		spin_lock_irqsave(&chan->lock, flags);
> -		req = virtqueue_get_buf(chan->vq, &len);
> -		if (req == NULL) {
> -			spin_unlock_irqrestore(&chan->lock, flags);
> -			break;
> +	spin_lock_irqsave(&chan->lock, flags);
> +	while ((req = virtqueue_get_buf(chan->vq, &len)) != NULL) {
> +		if (!chan->ring_bufs_avail) {
> +			chan->ring_bufs_avail = 1;
> +			need_wakeup = true;
>  		}
> -		chan->ring_bufs_avail = 1;
> -		spin_unlock_irqrestore(&chan->lock, flags);
> -		/* Wakeup if anyone waiting for VirtIO ring space. */
> -		wake_up(chan->vc_wq);
> +
>  		if (len)
>  			p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
>  	}
> +	spin_unlock_irqrestore(&chan->lock, flags);
> +	/* Wakeup if anyone waiting for VirtIO ring space. */
> +	if (need_wakeup)
> +		wake_up(chan->vc_wq);
>  }
> 
>  /**
>