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Re: New net features for added performance

To: Jeff Garzik <jgarzik@xxxxxxxxxxxxxxxx>
Subject: Re: New net features for added performance
From: Werner Almesberger <Werner.Almesberger@xxxxxxx>
Date: Sun, 25 Feb 2001 13:22:49 +0100
Cc: netdev@xxxxxxxxxxx, Linux Knernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
In-reply-to: <3A9842DC.B42ECD7A@xxxxxxxxxxxxxxxx>; from jgarzik@xxxxxxxxxxxxxxxx on Sat, Feb 24, 2001 at 06:25:16PM -0500
References: <3A9842DC.B42ECD7A@xxxxxxxxxxxxxxxx>
Sender: owner-netdev@xxxxxxxxxxx
Jeff Garzik wrote:
> 1) Rx Skb recycling.

Sounds like a potentially useful idea. To solve the most immediate memory
pressure problems, maybe VM could provide some function that does a kfree
in cases of memory shortage, and that does nothing otherwise, so the
driver could offer to free the skb after netif_rx. You still need to go
over the list in idle periods, though.

> 2) Tx packet grouping.

Hmm, I think we need an estimate of how long a packet train you'd usually
get. A flag looks reasonably inexpensive. Estimated numbers sound like

> Disadvantages?  Can this sort of knowledge be obtained by a netdevice
> right now, without any kernel modifications?

Question is what the hardware really needs. If you can change the
interrupt point easily, it's probably cheapest to do all the work in

> 3) Slabbier packet allocation.

Hmm, this may actually be worse during bursts: if you burst exceeds
the preallocated size, you have to perform more expensive/slower
operations (e.g. running a tasklet) to refill your cache.

- Werner

 / Werner Almesberger, ICA, EPFL, CH           Werner.Almesberger@xxxxxxx /

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