Date: Fri, 12 Sep 2003 17:22:54 +0100
From: Jamie Lokier <jamie@shareable.org>
To: Anthony Dominic Truong <anthony.truong@mascorp.com>
Cc: linux-kernel@vger.kernel.org, willy@debian.org
Subject: Re: Memory mapped IO vs Port IO
Message-ID: <20030912162254.GA2719@mail.jlokier.co.uk>
References: <20030911192550.7dfaf08c.ak@suse.de> <1063308053.4430.37.camel@huykhoi>
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Anthony Dominic Truong wrote:
> Wouldn't it be better if we set the IN and OUT function pointers to the
> right functions during driver init. based on the setting of dev->mmio.
> And throughout the driver, we just call the IN and OUT functions by
> their pointers.  Then we don't have to do if (dev->mmio) every time.
> It's similar to the concept of virtual member function in C++.

I think it would be faster to hide the "if (mmio)" part into an
inline function which calls one or the other, given a resource cookie.

Branch prediction will remove most of the cost of a conditional test,
which is always the same in these drivers after all, but I don't think
it's quite so good at predicting indirect function calls.

-- Jamie
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