From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [Xen-devel] [PATCH] xen-netback: Turn off the carrier if the guest is not able to receive Date: Mon, 4 Aug 2014 14:35:32 +0100 Message-ID: <53DF8C24.6030709@citrix.com> References: <1406749849-4356-1-git-send-email-zoltan.kiss@citrix.com> <1406749849-4356-2-git-send-email-zoltan.kiss@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: , , David Vrabel , To: Zoltan Kiss , Wei Liu , Ian Campbell Return-path: In-Reply-To: <1406749849-4356-2-git-send-email-zoltan.kiss@citrix.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 30/07/14 20:50, Zoltan Kiss wrote: > Currently when the guest is not able to receive more packets, qdisc layer starts > a timer, and when it goes off, qdisc is started again to deliver a packet again. > This is a very slow way to drain the queues, consumes unnecessary resources and > slows down other guests shutdown. > This patch change the behaviour by turning the carrier off when that timer > fires, so all the packets are freed up which were stucked waiting for that vif. > Instead of the rx_queue_purge bool it uses the VIF_STATUS_RX_PURGE_EVENT bit to > signal the thread that either the timout happened or an RX interrupt arrived, so > the thread can check what it should do. It also disables NAPI, so the guest > can't transmit, but leaves the interrupts on, so it can resurrect. I don't think you should disable NAPI, particularly since you have to fiddle with the bits directly instead of usign the API to do so. I looked at some hardware drivers and none of them disabled NAPI -- they just allow it to naturally end once hardware queues are drained. netback is a little different as a frontend could stop processing to-guest packets but continue sending from-guest ones. I don't see any problem with allowing this. > @@ -1955,24 +1955,78 @@ int xenvif_kthread_guest_rx(void *data) > */ > if (unlikely(queue->vif->disabled && queue->id == 0)) > xenvif_carrier_off(queue->vif); > + else if (unlikely(test_and_clear_bit(QUEUE_STATUS_RX_PURGE_EVENT, > + &queue->status))) { > + /* Either the last unsuccesful skb or at least 1 slot > + * should fit > + */ > + int needed = queue->rx_last_skb_slots ? > + queue->rx_last_skb_slots : 1; > > - if (kthread_should_stop()) > - break; > - > - if (queue->rx_queue_purge) { > + /* It is assumed that if the guest post new > + * slots after this, the RX interrupt will set > + * the bit and wake up the thread again > + */ > + set_bit(QUEUE_STATUS_RX_STALLED, &queue->status); This big if needs to go in a new function. David