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

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Message-ID: <CAErSpo6KyT=cnESwHL9cGaeGyC-XpHk7wi55Tp_Dw92WquEotg@mail.gmail.com>
Date:	Sat, 12 Jul 2014 11:31:36 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pci: Add include guard to include/linux/pci_ids.h

On Sat, Jul 12, 2014 at 6:09 AM, Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> 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.

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

Bjorn
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