netdev - RE: [PATCH net] xen-netback: correctly schedule rate-limited queues

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Date:   Wed, 21 Jun 2017 09:38:12 +0000
From:   Paul Durrant <Paul.Durrant@...rix.com>
To:     Wei Liu <wei.liu2@...rix.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Xen-devel <xen-devel@...ts.xenproject.org>,
        David Miller <davem@...emloft.net>,
        "jean-louis@...ond.be" <jean-louis@...ond.be>,
        Wei Liu <wei.liu2@...rix.com>
Subject: RE: [PATCH net] xen-netback: correctly schedule rate-limited queues

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@...rix.com]
> Sent: 21 June 2017 10:21
> To: netdev@...r.kernel.org
> Cc: Xen-devel <xen-devel@...ts.xenproject.org>; Paul Durrant
> <Paul.Durrant@...rix.com>; David Miller <davem@...emloft.net>; jean-
> louis@...ond.be; Wei Liu <wei.liu2@...rix.com>
> Subject: [PATCH net] xen-netback: correctly schedule rate-limited queues
> 
> Add a flag to indicate if a queue is rate-limited. Test the flag in
> NAPI poll handler and avoid rescheduling the queue if true, otherwise
> we risk locking up the host. The rescheduling will be done in the
> timer callback function.
> 
> Reported-by: Jean-Louis Dupond <jean-louis@...ond.be>
> Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> Tested-by: Jean-Louis Dupond <jean-louis@...ond.be>

Reviewed-by: Paul Durrant <paul.durrant@...rix.com>

> ---
>  drivers/net/xen-netback/common.h    | 1 +
>  drivers/net/xen-netback/interface.c | 6 +++++-
>  drivers/net/xen-netback/netback.c   | 6 +++++-
>  3 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-
> netback/common.h
> index 530586be05b4..5b1d2e8402d9 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -199,6 +199,7 @@ struct xenvif_queue { /* Per-queue data for xenvif */
>  	unsigned long   remaining_credit;
>  	struct timer_list credit_timeout;
>  	u64 credit_window_start;
> +	bool rate_limited;
> 
>  	/* Statistics */
>  	struct xenvif_stats stats;
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-
> netback/interface.c
> index 8397f6c92451..e322a862ddfe 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -106,7 +106,11 @@ static int xenvif_poll(struct napi_struct *napi, int
> budget)
> 
>  	if (work_done < budget) {
>  		napi_complete_done(napi, work_done);
> -		xenvif_napi_schedule_or_enable_events(queue);
> +		/* If the queue is rate-limited, it shall be
> +		 * rescheduled in the timer callback.
> +		 */
> +		if (likely(!queue->rate_limited))
> +			xenvif_napi_schedule_or_enable_events(queue);
>  	}
> 
>  	return work_done;
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> netback/netback.c
> index 602d408fa25e..5042ff8d449a 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -180,6 +180,7 @@ static void tx_add_credit(struct xenvif_queue
> *queue)
>  		max_credit = ULONG_MAX; /* wrapped: clamp to
> ULONG_MAX */
> 
>  	queue->remaining_credit = min(max_credit, max_burst);
> +	queue->rate_limited = false;
>  }
> 
>  void xenvif_tx_credit_callback(unsigned long data)
> @@ -686,8 +687,10 @@ static bool tx_credit_exceeded(struct xenvif_queue
> *queue, unsigned size)
>  		msecs_to_jiffies(queue->credit_usec / 1000);
> 
>  	/* Timer could already be pending in rare cases. */
> -	if (timer_pending(&queue->credit_timeout))
> +	if (timer_pending(&queue->credit_timeout)) {
> +		queue->rate_limited = true;
>  		return true;
> +	}
> 
>  	/* Passed the point where we can replenish credit? */
>  	if (time_after_eq64(now, next_credit)) {
> @@ -702,6 +705,7 @@ static bool tx_credit_exceeded(struct xenvif_queue
> *queue, unsigned size)
>  		mod_timer(&queue->credit_timeout,
>  			  next_credit);
>  		queue->credit_window_start = next_credit;
> +		queue->rate_limited = true;
> 
>  		return true;
>  	}
> --
> 2.11.0