netdev - Re: [PATCH] arm64: do_csum: implement accelerated scalar version

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Message-ID: <c14781ce-0fa5-bfc1-c019-bcfc07c42cc9@arm.com>
Date:   Fri, 16 Aug 2019 15:55:41 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Will Deacon <will.deacon@....com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        ilias.apalodimas@...aro.org,
        "huanglingyan (A)" <huanglingyan2@...wei.com>, steve.capper@....com
Subject: Re: [PATCH] arm64: do_csum: implement accelerated scalar version

On 16/08/2019 09:15, Shaokun Zhang wrote:
> Hi Will,
> 
> On 2019/8/16 0:46, Will Deacon wrote:
>> On Thu, May 16, 2019 at 11:14:35AM +0800, Zhangshaokun wrote:
>>> On 2019/5/15 17:47, Will Deacon wrote:
>>>> On Mon, Apr 15, 2019 at 07:18:22PM +0100, Robin Murphy wrote:
>>>>> On 12/04/2019 10:52, Will Deacon wrote:
>>>>>> I'm waiting for Robin to come back with numbers for a C implementation.
>>>>>>
>>>>>> Robin -- did you get anywhere with that?
>>>>>
>>>>> Still not what I would call finished, but where I've got so far (besides an
>>>>> increasingly elaborate test rig) is as below - it still wants some unrolling
>>>>> in the middle to really fly (and actual testing on BE), but the worst-case
>>>>> performance already equals or just beats this asm version on Cortex-A53 with
>>>>> GCC 7 (by virtue of being alignment-insensitive and branchless except for
>>>>> the loop). Unfortunately, the advantage of C code being instrumentable does
>>>>> also come around to bite me...
>>>>
>>>> Is there any interest from anybody in spinning a proper patch out of this?
>>>> Shaokun?
>>>
>>> HiSilicon's Kunpeng920(Hi1620) benefits from do_csum optimization, if Ard and
>>> Robin are ok, Lingyan or I can try to do it.
>>> Of course, if any guy posts the patch, we are happy to test it.
>>> Any will be ok.
>>
>> I don't mind who posts it, but Robin is super busy with SMMU stuff at the
>> moment so it probably makes more sense for you or Lingyan to do it.
> 
> Thanks for restarting this topic, I or Lingyan will do it soon.

FWIW, I've rolled up what I had so far and dumped it up into a quick 
semi-realistic patch here:

http://linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=859c5566510c32ae72039aa5072e932a771a3596

So far I'd put most of the effort into the aforementioned benchmarking 
harness to compare performance and correctness for all the proposed 
implementations over all reasonable alignment/length combinations - I 
think that got pretty much finished, but as Will says I'm unlikely to 
find time to properly look at this again for several weeks.

Robin.