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[Xen-devel] Re: [7/11] [NET] back: Added tx queue

On 27 Jul 2006, at 14:23, Herbert Xu wrote:

Also, what does NETIF_F_LLTX have to do with whether we have a queue or not -- couldn't we set that all the time? And you set queue length to 1

Sorry, should've add a comment about that. NETIF_F_LLTX is just an unused bit from the features set to indicate the fact that queueing is supported.
I suppose I could add a new flag too.

That's pretty gross. NETIF_F_LLTX is used isn't it? To indicate whether an interface does its own locking in start_xmit()?

Why not have a private feature flag in an appropriate netback-private structure?

in the other case -- what's wrong with zero? Seems a saner value when
there is no queue: or do we need to commit to having *some* queue at
register_netdevice() time, and there's no way to go back from that by
the time we find out if netfront supports rx refill notifications (so
at that point we cannot change queue len to zero)?

Exactly.  Once we've committed to having a queue, setting the queue
length to zero will cause all packets to be dropped.  I even added
a comment about that :)

Ok, sounds reasonable then.

But I would change queue length to 100 in your next spin of this patch. 1000 is scary big.

 -- Keir

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