From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752283AbaAOOwr (ORCPT ); Wed, 15 Jan 2014 09:52:47 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:26929 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751725AbaAOOwp (ORCPT ); Wed, 15 Jan 2014 09:52:45 -0500 X-IronPort-AV: E=Sophos;i="4.95,663,1384300800"; d="scan'208";a="90982437" Message-ID: <52D6A0B9.2030204@citrix.com> Date: Wed, 15 Jan 2014 14:52:41 +0000 From: Zoltan Kiss User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Wei Liu CC: , , , , Subject: Re: [PATCH net-next] xen-netback: Rework rx_work_todo References: <1389727719-21439-1-git-send-email-zoltan.kiss@citrix.com> <20140115103707.GI5698@zion.uk.xensource.com> <52D67536.4030106@citrix.com> <20140115144519.GO5698@zion.uk.xensource.com> In-Reply-To: <20140115144519.GO5698@zion.uk.xensource.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.133] X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/01/14 14:45, Wei Liu 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: >>>> > >>- xenvif_rx_action sets rx_queue_stopped to false >>>> > >>- interrupt happens, and sets rx_event to true >>>> > >>- then xenvif_kthread sets rx_event to false >>>> > >> >>> > > >>> > >If you mean "rx_work_todo" returns false. >>> > > >>> > >In this case >>> > > >>> > >(!skb_queue_empty(&vif->rx_queue) && !vif->rx_queue_stopped) || vif->rx_event; >>> > > >>> > >can still be true, can't it? >> >Sorry, I should wrote rx_queue_stopped to true >> > > In this case, if rx_queue_stopped is true, then we're expecting frontend > to notify us, right? > > rx_queue_stopped is set to true if we cannot make any progress to queue > packet into the ring. In that situation we can expect frontend will send > notification to backend after it goes through the backlog in the ring. > That means rx_event is set to true, and rx_work_todo is true again. So > the ring is actually not stalled in this case as well. Did I miss > something? > Yes, we expect the guest to notify us, and it does, and we set rx_event to true (see second point), but then the thread set it to false (see third point). Talking with Paul, another solution could be to set rx_event false before calling xenvif_rx_action. But using rx_last_skb_slots makes it quicker for the thread to see if it doesn't have to do anything. Zoli