From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zoltan Kiss Subject: Re: [PATCH net-next v2] xen-netback: Rework rx_work_todo Date: Mon, 20 Jan 2014 12:23:28 +0000 Message-ID: <52DD1540.7000503@citrix.com> References: <1389805867-22409-1-git-send-email-zoltan.kiss@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: Paul Durrant To: , , , , , Return-path: In-Reply-To: <1389805867-22409-1-git-send-email-zoltan.kiss@citrix.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Any reviews on this one? It fixes an important lockup situation, so either this or some other fix should go in soon. On 15/01/14 17:11, Zoltan Kiss wrote: > The recent patch to fix receive side flow control (11b57f) solved the spinning > thread problem, however caused an another one. The receive side can stall, if: > - [THREAD] xenvif_rx_action sets rx_queue_stopped to true > - [INTERRUPT] interrupt happens, and sets rx_event to true > - [THREAD] then xenvif_kthread sets rx_event to false > - [THREAD] rx_work_todo doesn't return true anymore > > Also, if interrupt sent but there is still no room in the ring, it take quite a > long time until xenvif_rx_action realize it. This patch ditch that two variable, > and rework rx_work_todo. If the thread finds it can't fit more skb's into the > ring, it saves the last slot estimation into rx_last_skb_slots, otherwise it's > kept as 0. Then rx_work_todo will check if: > - there is something to send to the ring (like before) > - there is space for the topmost packet in the queue > > I think that's more natural and optimal thing to test than two bool which are > set somewhere else. > > Signed-off-by: Zoltan Kiss > --- > drivers/net/xen-netback/common.h | 6 +----- > drivers/net/xen-netback/interface.c | 1 - > drivers/net/xen-netback/netback.c | 16 ++++++---------- > 3 files changed, 7 insertions(+), 16 deletions(-) > > diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h > index 4c76bcb..ae413a2 100644 > --- a/drivers/net/xen-netback/common.h > +++ b/drivers/net/xen-netback/common.h > @@ -143,11 +143,7 @@ struct xenvif { > char rx_irq_name[IFNAMSIZ+4]; /* DEVNAME-rx */ > struct xen_netif_rx_back_ring rx; > struct sk_buff_head rx_queue; > - bool rx_queue_stopped; > - /* Set when the RX interrupt is triggered by the frontend. > - * The worker thread may need to wake the queue. > - */ > - bool rx_event; > + RING_IDX rx_last_skb_slots; > > /* This array is allocated seperately as it is large */ > struct gnttab_copy *grant_copy_op; > diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c > index b9de31e..7669d49 100644 > --- a/drivers/net/xen-netback/interface.c > +++ b/drivers/net/xen-netback/interface.c > @@ -100,7 +100,6 @@ static irqreturn_t xenvif_rx_interrupt(int irq, void *dev_id) > { > struct xenvif *vif = dev_id; > > - vif->rx_event = true; > xenvif_kick_thread(vif); > > return IRQ_HANDLED; > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c > index 2738563..bb241d0 100644 > --- a/drivers/net/xen-netback/netback.c > +++ b/drivers/net/xen-netback/netback.c > @@ -477,7 +477,6 @@ static void xenvif_rx_action(struct xenvif *vif) > unsigned long offset; > struct skb_cb_overlay *sco; > bool need_to_notify = false; > - bool ring_full = false; > > struct netrx_pending_operations npo = { > .copy = vif->grant_copy_op, > @@ -487,7 +486,7 @@ static void xenvif_rx_action(struct xenvif *vif) > skb_queue_head_init(&rxq); > > while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) { > - int max_slots_needed; > + RING_IDX max_slots_needed; > int i; > > /* We need a cheap worse case estimate for the number of > @@ -510,9 +509,10 @@ static void xenvif_rx_action(struct xenvif *vif) > if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) { > skb_queue_head(&vif->rx_queue, skb); > need_to_notify = true; > - ring_full = true; > + vif->rx_last_skb_slots = max_slots_needed; > break; > - } > + } else > + vif->rx_last_skb_slots = 0; > > sco = (struct skb_cb_overlay *)skb->cb; > sco->meta_slots_used = xenvif_gop_skb(skb, &npo); > @@ -523,8 +523,6 @@ static void xenvif_rx_action(struct xenvif *vif) > > BUG_ON(npo.meta_prod > ARRAY_SIZE(vif->meta)); > > - vif->rx_queue_stopped = !npo.copy_prod && ring_full; > - > if (!npo.copy_prod) > goto done; > > @@ -1727,8 +1725,8 @@ static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif, > > static inline int rx_work_todo(struct xenvif *vif) > { > - return (!skb_queue_empty(&vif->rx_queue) && !vif->rx_queue_stopped) || > - vif->rx_event; > + return !skb_queue_empty(&vif->rx_queue) && > + xenvif_rx_ring_slots_available(vif, vif->rx_last_skb_slots); > } > > static inline int tx_work_todo(struct xenvif *vif) > @@ -1814,8 +1812,6 @@ int xenvif_kthread(void *data) > if (!skb_queue_empty(&vif->rx_queue)) > xenvif_rx_action(vif); > > - vif->rx_event = false; > - > if (skb_queue_empty(&vif->rx_queue) && > netif_queue_stopped(vif->dev)) > xenvif_start_queue(vif); >