Re: [RFC PATCH] aarch64: improve memset

[Richard Henderson <rth at twiddle dot net>]

On 11/07/2014 05:14 PM, Wilco Dijkstra 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.
> 
> * 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.


Here's a version which only implements zva for 64 and 128-byte line sizes.

It also removes the version that loaded the zva data each time, which had
been used by ld.so and no-ifunc.  That was the path I had been concerned
about back in September.

That leaves ld.so using the no-zva path, which is perhaps a tad unfortunate
given that it needs to zero partial .bss pages during startup, and on a
system with 64k pages, we probably wind up with larger clears more often
than not...

Thoughts?


r~

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