Re: [Xen-devel] [PATCH net] xen-netback: correctly schedule rate-limited queues

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 21 June 2017 10:21
> To: netdev@xxxxxxxxxxxxxxx
> Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Paul Durrant
> <Paul.Durrant@xxxxxxxxxx>; David Miller <davem@xxxxxxxxxxxxx>; jean-
> louis@xxxxxxxxx; Wei Liu <wei.liu2@xxxxxxxxxx>
> 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@xxxxxxxxx>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Tested-by: Jean-Louis Dupond <jean-louis@xxxxxxxxx>

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

> ---
>  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


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