Re: [RFC PATCH] aarch64: improve memset

[Andrew Pinski <pinskia at gmail dot com>]

On Tue, Nov 11, 2014 at 5:05 AM, Marcus Shawcroft
<marcus.shawcroft@gmail.com> wrote:
> On 7 November 2014 16:14, Wilco Dijkstra <wdijkstr@arm.com> wrote:
>>> Richard Henderson wrote:
>
>> I've got a few comments on this patch:
>>
>> * Do we really need variants for cache line sizes that are never going to be used?
>>   I'd say just support 64 and 128, and default higher sizes to no_zva.
>
> We shouldn't be removing support for the other sizes already supported
> by the existing implementation.  If the other sizes were deprecated
> from the architecture then fair game, but that is not the case.  From
> offline conversation with Wilco I gather part of the motivation to
> remove is that the none 64  cases cannot be readily tested on HW.
> That particular issue was solved in the original implementation using
> a hacked qemu.

I will have the ability to test on hardware which uses 128 byte case
soon.  I already testing using a simulator which sets it to 128 byte
(though I use it for performance analysis though).

Thanks,
Andrew


>
> Cheers
> /Marcus
>
>> * Why special case line size=64 only? Unrolling might not help for 128 but should not
>>   harm either, and the alignment overhead only increases with larger line sizes, so you
>>   want to bypass the zva code in all cases if N < 3-4x line size.
>>
>> * Is the no-ifunc variant still required/used? We're now having at least 4 different
>>   variants which all need to be tested and maintained...
>>
>> * Finally, which version is used when linking statically? I presume there is some
>>   makefile magic that causes the no-zva version to be used, however that might not be
>>   optimal for all targets.
>>
>> Wilco
>>
>>