Re: [PATCH -next 2/2] virtio_net: Read the advised MTU

Hi Rick,

In the future, please don't cut the list.

Rick Jones [off-list ref] writes:

On 06/02/2016 08:43 AM, Aaron Conole wrote:

quoted

This patch checks the feature bit for the VIRTIO_NET_F_MTU feature. If it
exists, read the advised MTU and use it.

No proper error handling is provided for the case where a user changes the
negotiated MTU. A future commit will add proper error handling. Instead, a
warning is emitted if the guest changes the device MTU after previously
being given advice.

One of the things I've been doing has been setting-up a cluster
(OpenStack) with JumboFrames, and then setting MTUs on instance vNICs
by hand to measure different MTU sizes.  It would be a shame if such a
thing were not possible in the future.  Keeping a warning if shrinking
the MTU would be good, leave the error (perhaps) to if an attempt is
made to go beyond the advised value.

This was cut because it didn't make sense for such a warning to
be issued, but it seems like perhaps you may want such a feature?  I
agree with Michael, after thinking about it, that I don't know what sort
of use the warning would serve.  After all, if you're changing the MTU,
you must have wanted such a change to occur?

-Aaron

happy benchmarking,

rick jones

On 06/02/2016 10:06 AM, Aaron Conole wrote:

Rick Jones [off-list ref] writes:

quoted

One of the things I've been doing has been setting-up a cluster
(OpenStack) with JumboFrames, and then setting MTUs on instance vNICs
by hand to measure different MTU sizes.  It would be a shame if such a
thing were not possible in the future.  Keeping a warning if shrinking
the MTU would be good, leave the error (perhaps) to if an attempt is
made to go beyond the advised value.

This was cut because it didn't make sense for such a warning to
be issued, but it seems like perhaps you may want such a feature?  I
agree with Michael, after thinking about it, that I don't know what sort
of use the warning would serve.  After all, if you're changing the MTU,
you must have wanted such a change to occur?

I don't need a warning, was simply willing to live with one when 
shrinking the MTU.  Didn't want an error.

happy benchmarking,

rick jones