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Re: Giving priority to messages

To: Donald Becker <becker@xxxxxxxxx>
Subject: Re: Giving priority to messages
From: jamal <hadi@xxxxxxxxxx>
Date: Tue, 19 Sep 2000 22:34:54 -0400 (EDT)
Cc: Andi Kleen <ak@xxxxxx>, Ramón Agüero <ramon@xxxxxxxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <Pine.LNX.4.10.10009192217060.1031-100000@xxxxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx

On Tue, 19 Sep 2000, Donald Becker wrote:

> This is one of the reasons for drivers to keep their Tx queues to a
> reasonable length.  Two years ago an almost-always-sufficient Tx queue
> length was between 6 and 10, so most of my bus-master drivers use a queue
> length of 10.  Ten 1500 byte packets at 10Mbps is still not too long, but
> ten 60 byte packets (approx. 96 byte periods on the wire) isn't very long at
> 100Mbps.
> 
> If you care *that* *much* about priority and scheduling, you are probably
> wrong about what you want.  We did some work on utilizing the real-time
> transmit scheduling in the 3Com hardware, and found out that it made almost
> zero difference to [[the multimedia application we were testing]].

Donald,

The Tulip, for example, can have its DMA buffers stashed in a linked list
instead of a ring structure.
Maybe not the most efficient scheme but could you could play with
priority queueing structures/algorithms for the DMA buffers in this
case and for example stick a higher priority packet to the head of the
queue? I have not implemented any such thing, just thinking out
loudly. 

cheers,
jamal


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