linux-kernel - Re: [RFC PATCH 0/7] Improve swiotlb performance by using physical addresses

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Message-ID: <5074756C.8070502@intel.com>
Date:	Tue, 09 Oct 2012 12:05:16 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	konrad.wilk@...cle.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, rob@...dley.net, akpm@...ux-foundation.org,
	joerg.roedel@....com, bhelgaas@...gle.com, shuahkhan@...il.com,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	x86@...nel.org, torvalds@...ux-foundation.org
Subject: Re: [RFC PATCH 0/7] Improve swiotlb performance by using physical
 addresses

On 10/08/2012 08:43 AM, Alexander Duyck wrote:
> On 10/06/2012 10:57 AM, Andi Kleen wrote:
>> BTW __pa used to be a simple subtraction, the if () was just added to
>> handle the few call sites for x86-64 that do __pa(&text_symbol).
>> Maybe we should just go back to the old __pa_symbol() for those cases,
>> then __pa could be the simple subtraction it used to was again
>> and it could be inlined and everyone would be happy.
>>
>> -Andi
> What I am probably looking at doing is splitting the function in two as
> you suggest where we have a separate function for the text symbol case. 
> I will probably also take the 32 bit approach and add a debug version
> that is still a separate function for uses such as determining if we
> have any callers who should be using __pa_symbol instead of __pa.
>
> Thanks,
>
> Alex

I gave up on trying to split __pa and __pa_symbol.   Yesterday I
realized there is way too much code that depends on the two resolving to
the same function, and many cases are pretty well hidden.  Instead I
just mailed out a patch that inlines an optimized version of
__phys_addr.  I figure it is probably as good as it is going to get
without having to rip the entire x86 portion of the kernel apart to
separate uses of __pa and __pa_symbol.

Thanks,

Alex
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