netdev - Re: [PATCH] stmmac: reduce queue lengths if MTU is very large

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Message-Id: <20111220.134120.1764634344589128309.davem@davemloft.net>
Date:	Tue, 20 Dec 2011 13:41:20 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	rubini@...dd.com
Cc:	peppe.cavallaro@...com, netdev@...r.kernel.org,
	giancarlo.asnaghi@...com
Subject: Re: [PATCH] stmmac: reduce queue lengths if MTU is very large

From: Alessandro Rubini <rubini@...dd.com>
Date: Tue, 20 Dec 2011 08:30:50 +0100

> Allocation of the queues is based on a parameter. If the parameter was
> a size, instead of a lenght, all would be fine, wouldn't it? If you
> agree, then this patch is turning the lenght into a size, in a way.

That doesn't make any sense either, queues are sized by TX descriptor
slots not bytes.

> Now, how could we deal with the fact that the size explodes if the MTU
> is increased?

Maybe... set the initial parameter appropriately?  This is enormously
better than fixing it up after the fact.

Maybe I set the number of TX entries based upon my expected packet
load of small packets.  If I happen to set my MTU to 9000 that's
irrelevant to the setting.

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