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Date: Mon, 28 Nov 2016 11:28:23 -0500 (EST) From: David Miller <davem@...emloft.net> To: mst@...hat.com Cc: jasowang@...hat.com, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, hannes@...hat.com, nhorman@...hat.com, jeder@...hat.com, myllynen@...hat.com, maxime.coquelin@...hat.com Subject: Re: [PATCH net-next] virtio-net: enable multiqueue by default From: "Michael S. Tsirkin" <mst@...hat.com> 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 <hannes@...hat.com> >> Cc: Michael S. Tsirkin <mst@...hat.com> >> Cc: Neil Horman <nhorman@...hat.com> >> Cc: Jeremy Eder <jeder@...hat.com> >> Cc: Marko Myllynen <myllynen@...hat.com> >> Cc: Maxime Coquelin <maxime.coquelin@...hat.com> >> Signed-off-by: Jason Wang <jasowang@...hat.com> > > 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.
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