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

[Siddhesh Poyarekar]

On Thursday 12 October 2017 03:14 AM, Andrew Pinski wrote:
> For at least the micro-archs I work with, reading dczid_el0 can and
> will most likely be faster than reading from global memory.
> Especially if the global memory is not in the L1 cache.  This is one
> case where a micro-benchmark can fall down.  If the global memory is
> in L1 cache the read is 3 cycles while reading from dczid_el0 is 4
> cycles, but once it is out of L1 cache, reading becomes 10x worse plus
> it pollutes the L1 cache.

This is a falkor caveat - mrs ends up being significantly slower.  Also,
the question about reading a global is pointless since I've dropped that
code path.  It only affected non-standard zva sizes anyway so it doesn't
affect current cores.

Siddhesh