Re: [PATCH] pci: Add include guard to include/linux/pci_ids.h

From: Bjorn Helgaas
Date: Sat Jul 12 2014 - 13:32:13 EST

On Sat, Jul 12, 2014 at 6:09 AM, Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:
> Bjorn Helgaas <bhelgaas@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
>> 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.

Yeah, changing 800 files for a minor build performance improvement
doesn't sound like it'd be worth the churn.

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