netdev - RE: [PATCH (net-next.git) 13/18] stmmac: perf, remove modulo in stmmac

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Date:	Wed, 9 Dec 2015 17:21:34 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Giuseppe Cavallaro' <peppe.cavallaro@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"alexandre.torgue@...com" <alexandre.torgue@...com>,
	Fabrice Gasnier <fabrice.gasnier@...com>
Subject: RE: [PATCH (net-next.git) 13/18] stmmac: perf, remove modulo in
 stmmac_rx()

From: Giuseppe Cavallaro
> Sent: 09 December 2015 08:38
> The indexes into the ring buffer are always incremented, and
> the entry is accessed via doing a modulo to find the "real" index.
> Modulo is an expensive operation.
> 
> This patch replaces the modulo with a simple if clamp.
> It helps improve stmmac RX path as it's being called inside RX loop.

Is dma_rx_size always a power of 2 ?
If so you can replace the % by & and remove the conditionals.

If you have changed the read and write values to indexes
then you need to be certain that the 'ring full' and 'ring empty'
cases are correctly distinguished.

	David
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