From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next] virtio-net: enable multiqueue by default Date: Mon, 28 Nov 2016 11:28:23 -0500 (EST) Message-ID: <20161128.112823.2263657283777032168.davem@davemloft.net> References: <1480048646-17536-1-git-send-email-jasowang@redhat.com> <20161125064201-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: nhorman@redhat.com, jeder@redhat.com, hannes@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, myllynen@redhat.com, maxime.coquelin@redhat.com To: mst@redhat.com Return-path: In-Reply-To: <20161125064201-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org From: "Michael S. Tsirkin" Date: Fri, 25 Nov 2016 06:43:08 +0200 > On Fri, Nov 25, 2016 at 12:37:26PM +0800, Jason Wang wrote: >> We use single queue even if multiqueue is enabled and let admin to >> enable it through ethtool later. This is used to avoid possible >> regression (small packet TCP stream transmission). But looks like an >> overkill since: >> >> - single queue user can disable multiqueue when launching qemu >> - brings extra troubles for the management since it needs extra admin >> tool in guest to enable multiqueue >> - multiqueue performs much better than single queue in most of the >> cases >> >> So this patch enables multiqueue by default: if #queues is less than or >> equal to #vcpu, enable as much as queue pairs; if #queues is greater >> than #vcpu, enable #vcpu queue pairs. >> >> Cc: Hannes Frederic Sowa >> Cc: Michael S. Tsirkin >> Cc: Neil Horman >> Cc: Jeremy Eder >> Cc: Marko Myllynen >> Cc: Maxime Coquelin >> Signed-off-by: Jason Wang > > OK at some level but all uses of num_online_cpus() > like this are racy versus hotplug. > I know we already have this bug but shouldn't we fix it > before we add more? This is more being used like a heuristic in this scenerio, and in fact I would say one would keep the code this way even once proper hotplug handlers are installed to adjust the queued dynamically if there is a desired (which is also not necessarily the case). I really don't think this change should be held on up on this issue. So can we please make some forward progress here? Thanks.