linux-kernel - Re: [PATCH] net: fec: fix regression on i.MX28 introduced by rx

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Message-ID: <20141008091248.GE5182@n2100.arm.linux.org.uk>
Date:	Wed, 8 Oct 2014 10:12:48 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	'Sergei Shtylyov' <sergei.shtylyov@...entembedded.com>,
	Lothar Waßmann <LW@...O-electronics.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Frank Li <Frank.Li@...escale.com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: fec: fix regression on i.MX28 introduced by
	rx_copybreak support

On Wed, Oct 08, 2014 at 08:54:58AM +0000, David Laight wrote:
> Hmmm... in that case you may not want the compiler to convert the bit value
> to a 'bool' at all.
> 
> Passing 'id_entry->driver_data' through (that doesn't look like a field name for
> 'quirk flags) would generate better code.
> 
> Even better would be to reference the flag directly from 'ndev'.
> A pointer indirection for the test if probably faster then passing
> another argument.

A far better idea would be to copy the quirks into the fec_net_private
structure, storing them as a 'unsigned int' value, and test them from
there.  This is /much/ more efficient than jumping through the hoops to
retrieve id_entry, and then testing the 64-bit driver_data value.

I've had such a patch since about the beginning of the year (and patches
which add stuff like byte queue limits, which are really needed now that
we have a /huge/ transmit ring), but I can't keep up with rebasing the
patch set, and properly tested and performance impacts evaluated due to
the rate of FEC changes.  I never finished rebasing the set after Andy's
TSO work...

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