linux-kernel - Re: [PATCH] x86: Improve 64 bit __phys

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Date:	Wed, 10 Oct 2012 16:56:25 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86: Improve 64 bit __phys_addr call performance

On 10/10/2012 06:58 AM, Andi Kleen wrote:
>> The second change was to streamline the code by making use of the carry flag
>> on an add operation instead of performing a compare on a 64 bit value.  The
>> advantage to this is that it allows us to reduce the overall size of the call.
>> On my Xeon E5 system the entire __phys_addr inline call consumes 30 bytes and
>> 5 instructions.  I also applied similar logic to the debug version of the
>> function.  My testing shows that the debug version of the function with this
>> patch applied is slightly faster than the non-debug version without the patch.
> Looks good. Thanks. 
>
> Probably should still split the callers though (or have a pa_symbol_fast
> that does not do the check)
>
> -Andi

I hadn't thought of that.  I couldn't drop support for symbols from
__pa, but I can get away with dropping support for regular addresses
from __pa_symbol.

I just submitted a patch to drop support for standard virtual addresses
from __pa_symbol.  I will also submit some patches tomorrow morning for
cleaning up a number of places I had found where we were calling
__pa/virt_to_phys when we should have been calling __pa_symbol.

Thanks,

Alex
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