netdev - Re: [PATCH v2 net-next] net: Implement fast csum_partial for x86

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Message-ID: <CALx6S375Z1SqnS1DHj4FOsQGrLeeBPTzQx=v_2c5EFiUFWyAtQ@mail.gmail.com>
Date:	Wed, 6 Jan 2016 18:36:54 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Kernel Team <kernel-team@...com>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org
Subject: Re: [PATCH v2 net-next] net: Implement fast csum_partial for x86_64

On Wed, Jan 6, 2016 at 5:52 PM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> Hi Tom,
>
> On 05.01.2016 19:41, Tom Herbert wrote:
>>
>> --- /dev/null
>> +++ b/arch/x86/lib/csum-partial_64.S
>> @@ -0,0 +1,147 @@
>> +/* Copyright 2016 Tom Herbert <tom@...bertland.com>
>> + *
>> + * Checksum partial calculation
>> + *
>> + * __wsum csum_partial(const void *buff, int len, __wsum sum)
>> + *
>> + * Computes the checksum of a memory block at buff, length len,
>> + * and adds in "sum" (32-bit)
>> + *
>> + * Returns a 32-bit number suitable for feeding into itself
>> + * or csum_tcpudp_magic
>> + *
>> + * Register usage:
>> + *   %rdi: argument 1, buff
>> + *   %rsi: argument 2, length
>> + *   %rdx: argument 3, add in value
>
>
> I think you forgot to carry-add-in the %rdx register.
>
> The assembly code replaces do_csum but not csum_partial.
>
First instruction is: movl    %edx, %eax      /* Initialize with
initial sum argument */

Tom

> Bye,
> Hannes
>
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