Re: [PING][PATCHv3 1/2] aarch64: Hoist ZVA check out of the memset function

[Szabolcs Nagy <szabolcs dot nagy at arm dot com>]

On 12/10/17 02:48, Siddhesh Poyarekar wrote:
> [I've responded to your point about macros elsewhere in the thread]
> 
> On Thursday 12 October 2017 02:50 AM, Wilco Dijkstra wrote:
>> Note we also should benchmark this on various other cores to see what
>> the impact is. I wrote this memset code for specific reasons - changing that
>> could have a big impact on some cores, so we need to show this doesn't
>> cause regressions.
> 
> Yes, and that's something I'll lean on you to study and fix since I
> don't have access to all that hardware :)
> 
> That said, the effect of dropping zva checks should be positive on every
> core for memset(0).  The alignments might change things a bit but I
> think we should fix those as we go along and not wait for that to be
> correct since this gain is pretty big to keep away.  This also adds
> incentive to document our alignment decisions since they weren't
> documented in the earlier code.
> 

since the patch modifies the memset code that runs in
most cases, the impact of the change should be well
understood before it goes in.

in the static linked case it will introduce a plt
indirection, i don't expect a big gain except on falkor
and there is a risk of regression on other cores, it
also makes the code less maintainable.

we should not be in a hurry applying such patches.