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Re: [Qemu-devel] [PATCH v3 2/2] net: introduce command to query rx-filte

From: Luiz Capitulino
Subject: Re: [Qemu-devel] [PATCH v3 2/2] net: introduce command to query rx-filter information
Date: Fri, 24 May 2013 09:08:34 -0400

On Fri, 24 May 2013 06:55:44 -0600
Eric Blake <address@hidden> wrote:

> On 05/24/2013 06:23 AM, Luiz Capitulino wrote:
> >>> I don't think we need this argument. This command is quite simple in its
> >>> response, let's do this filtering in HMP only.
> >>
> >> Event message contains the net client name, management might only want
> >> to query the single net client.
> > 
> > The client can do the filtering itself.
> If we're arguing that we want this to be as responsive as possible, then
> the less data we send over the wire, the faster management can react to
> the guest's request for a particular NIC.  That is, if libvirt is
> listening to events that says NIC2 wants to change rx-filter, libvirt
> would rather do a filtered query where it knows the JSON array of 1
> element matches NIC2 data, rather than do a global query and search
> through the returned array until it finds NIC2.

This sounds like premature optimization to me, but I wonder if instead
of cluttering commands with arguments to do the filtering we could add
some standard way of doing this in the QAPI.

It was you who suggested a filter command?

> Filtering is relatively easy to add, whether you do it in QMP or make
> every client add it.  Libvirt will survive if you don't have filtering,
> but I don't see why we can't have it in QMP.  Also, if you DO decide to
> rip filtering out of QMP, you STILL need to keep a per-NIC flag.  Since
> the events say which NIC is requesting a change, even if the query reads
> all nics, libvirt will only change the macvtap settings of the nic(s)
> for which it has received an event (it doesn't make sense to waste time
> requesting a (no-op) change to macvtap settings on a nic that hasn't
> requested a change).  But if you argue that having no filtering in the
> QMP command means that you can get away with a single flag instead of a
> per-nic flag, then you will fail to emit an event for NIC2 if it changes
> in between the time that NIC1 fired an event and libvirt finally does
> the query, and libvirt wouldn't realize that NIC2 also needs a macvtap
> change.

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