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

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: [Xen-devel] Re: [7/11] [NET] back: Added tx queue
From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 27 Jul 2006 23:23:46 +1000
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On Thu, Jul 27, 2006 at 02:15:29PM +0100, Keir Fraser wrote:
> What's the default queue size? It shouldn't be too large if each packet 
> can be 64kB!

The default is 1000.  If 64MB is too much for each domain, then how about

> 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.

> 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 :)

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