linux-kernel - Re: [PATCH] pci: Add include guard to include/linux/pci

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Date:	Sat, 12 Jul 2014 14:09:18 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci: Add include guard to include/linux/pci_ids.h

Bjorn Helgaas <bhelgaas@...gle.com> writes:

> On Thu, Jul 10, 2014 at 02:05:11PM +0200, Rasmus Villemoes wrote:
>> Adding an include guard frees the preprocessor from reparsing over
>> 2600 #defines in the cases where pci_ids.h is somehow included more
>> than once. This gives a tiny-but-measurable performance improvement
>> when compiling such files.
>> 
>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>
> Applied to pci/misc for v3.17, thanks!
>

Great.

One thing I thought about, but which is likely undoable in practice:
There are only about 800 files which use any of the #defines in
pci_ids.h, but more than 3000 files include pci.h directly or
indirectly. Making those 800 include pci_ids.h directly and removing it
from pci.h could speed up compilation of the other 2200.

Rasmus
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