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Subject: Re: [virtio-comment] Re: [PATCH v2] virtio-net: support the virtqueue coalescing moderation
On Sat, Feb 11, 2023 at 12:18:45PM +0200, Alvaro Karsz wrote: > > >> Please add short description something like, > > >> > > >> When the driver prefers to use per virtqueue notifications coalescing, and if queue group (transmit or receive) level notification coalescing is enabled, driver SHOULD first disable device level notification coalescing. > > >> Or it should be, > > >> > > > I disagree here. > > > IMO "queue group level notification coalescing" is not something to > > > enable or disable, but a shortcut to set all TX/RX queues at once. > > > Why should the spec force a driver to "disable device level > > > notification coalescing" (I assume you mean send a > > > VIRTIO_NET_CTRL_NOTF_COAL_[T/R]X_SET command with zeros)? > > > What if the driver sends a VIRTIO_NET_CTRL_NOTF_COAL_[T/R]X_SET > > > command, and then a single queue traffic increases? why should it zero > > > the parameters to all other queues? > > > > Hi, Alvaro! Thanks for your reply! > > > > I think Parav refers more to the scene where ethool sets parameters at > > the queue group level and > > the scene where netdim sets parameters for a single queue. In this > > scenario, netdim should really > > determine the coalescing parameters of the device, and the parameters at > > the queue group level set > > by ethtool should be ignored (many drivers are designed this way, such > > as mlx), that is, we need to give netdim the right, > > because it It has the ability to dynamically adjust parameters. > > (However, I think this friendly constraint is also possible in driver > > implementation.) > > > > Of course, if we consider setting coalescing parameters at the queue > > group level and single queue level separately through ethtool, > > then as you said, we should not set any priority for them. > > > > Back to reality, I think the function of ethtool to set single queue > > parameters may come later, which is thankless for users because of netdim. > > > > Therefore, if our specification tends to be practical, we can add > > Parav's proposal, and if our specification tends to be more general, > > then hand over > > the constraints to the driver implementation. what do you think? > > Hi, > I understand your and Parav's point, and that this is needed for netdim. > I just think that the spec should not dictate this, and this should be > implementation specific. > What if a OS with a different adaptive functionality wants to support > these features? > > This is just my opinion though. I'm not sure the specific property is even a feature and not a bug. One can argue e.g. that ethtool should fail with EBUSY rather than being silently overwritten. Thats why I feel this kind of policy is best set by driver. -- MST
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