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Message-ID: <20230510012951-mutt-send-email-mst@kernel.org> Date: Wed, 10 May 2023 01:32:53 -0400 From: "Michael S. Tsirkin" <mst@...hat.com> To: Jason Wang <jasowang@...hat.com> Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, maxime.coquelin@...hat.com, alvaro.karsz@...id-run.com, eperezma@...hat.com, xuanzhuo@...ux.alibaba.com, david.marchand@...hat.com, netdev <netdev@...r.kernel.org> Subject: Re: [PATCH net-next V2 1/2] virtio-net: convert rx mode setting to use workqueue On Mon, Apr 17, 2023 at 11:40:58AM +0800, Jason Wang wrote: > On Fri, Apr 14, 2023 at 3:21 PM Michael S. Tsirkin <mst@...hat.com> wrote: > > > > On Fri, Apr 14, 2023 at 01:04:15PM +0800, Jason Wang wrote: > > > Forget to cc netdev, adding. > > > > > > On Fri, Apr 14, 2023 at 12:25 AM Michael S. Tsirkin <mst@...hat.com> wrote: > > > > > > > > On Thu, Apr 13, 2023 at 02:40:26PM +0800, Jason Wang wrote: > > > > > This patch convert rx mode setting to be done in a workqueue, this is > > > > > a must for allow to sleep when waiting for the cvq command to > > > > > response since current code is executed under addr spin lock. > > > > > > > > > > Signed-off-by: Jason Wang <jasowang@...hat.com> > > > > > > > > I don't like this frankly. This means that setting RX mode which would > > > > previously be reliable, now becomes unreliable. > > > > > > It is "unreliable" by design: > > > > > > void (*ndo_set_rx_mode)(struct net_device *dev); > > > > > > > - first of all configuration is no longer immediate > > > > > > Is immediate a hard requirement? I can see a workqueue is used at least: > > > > > > mlx5e, ipoib, efx, ... > > > > > > > and there is no way for driver to find out when > > > > it actually took effect > > > > > > But we know rx mode is best effort e.g it doesn't support vhost and we > > > survive from this for years. > > > > > > > - second, if device fails command, this is also not > > > > propagated to driver, again no way for driver to find out > > > > > > > > VDUSE needs to be fixed to do tricks to fix this > > > > without breaking normal drivers. > > > > > > It's not specific to VDUSE. For example, when using virtio-net in the > > > UP environment with any software cvq (like mlx5 via vDPA or cma > > > transport). > > > > > > Thanks > > > > Hmm. Can we differentiate between these use-cases? > > It doesn't look easy since we are drivers for virtio bus. Underlayer > details were hidden from virtio-net. > > Or do you have any ideas on this? > > Thanks I don't know, pass some kind of flag in struct virtqueue? "bool slow; /* This vq can be very slow sometimes. Don't wait for it! */" ? -- MST
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