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From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] arm64: Implement optimised IP checksum helpers
Date: Tue, 31 May 2016 15:39:06 +0100	[thread overview]
Message-ID: <574DA20A.4070302@arm.com> (raw)
In-Reply-To: <574D9E8F.7080509@arm.com>

Hi James,

On 31/05/16 15:24, James Morse wrote:
> Hi Robin,
>
> On 31/05/16 12:22, Robin Murphy wrote:
>> AArch64 is capable of 128-bit memory accesses without alignment
>> restrictions, which makes it both possible and highly practical to slurp
>> up a typical 20-byte IP header in just 2 loads. Implement our own
>> version of ip_fast_checksum() to take advantage of that, resulting in
>> considerably fewer instructions and memory accesses than the generic
>> version. We can also get more optimal code generation for csum_fold() by
>> defining it a slightly different way round from the generic version, so
>> throw that into the mix too.
>>
>> Suggested-by: Luke Starrett <luke.starrett@broadcom.com>
>> Acked-by: Luke Starrett <luke.starrett@broadcom.com>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>
>> Minor changes: include types.h for correctness, add Luke's ack.
>>
>>   arch/arm64/include/asm/checksum.h | 51 +++++++++++++++++++++++++++++++++++++++
>
> Maybe a nit, don't you need to remove the 'generic-y += checksum.h' line from
> arch/arm64/include/asm/Kbuild to avoid the generated version being created too? [0]

I guess you skimmed the very end of the patch ;)

+#include <asm-generic/checksum.h>

> The compiler on my box picks your header in preference to the generated one, but
> [1] suggests it isn't to be trusted!

We only cherry-pick a couple of functions to optimise, so not building 
the generic file would necessitate copy-pasting the rest of it. I'd hope 
this pattern is sufficiently robust, since it's already in use on a 
number of other architectures! AFAICS [1] only applies when the generic 
file shouldn't be built at all, so cross fingers we're probably OK.

Robin.

> Thanks,
>
> James
>
> [0] d8ecc5cd8e22 ("kbuild: asm-generic support")
> [1] https://lkml.org/lkml/2016/5/23/78
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

  reply	other threads:[~2016-05-31 14:39 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-31 11:22 [PATCH v2] arm64: Implement optimised IP checksum helpers Robin Murphy
2016-05-31 14:24 ` James Morse
2016-05-31 14:39   ` Robin Murphy [this message]
2016-05-31 14:43     ` Robin Murphy
2016-05-31 17:04 ` [PATCH v3] " Robin Murphy
2016-05-31 23:30   ` Goel, Sameer
2016-06-17 17:02   ` Catalin Marinas

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