[PATCH 2/2] Ignore prefetcher tagging for smaller copies

[Szabolcs Nagy]

On 03/05/18 18:52, Siddhesh Poyarekar wrote:
> For smaller and medium sized copies, the effect of hardware
> prefetching are not as dominant as instruction level parallelism.
> Hence it makes more sense to load data into multiple registers than to
> try and route them to the same prefetch unit.  This is also the case
> for the loop exit where we are unable to latch on to the same prefetch
> unit anyway so it makes more sense to have data loaded in parallel.
> 
> The performance results are a bit mixed with memcpy-random, with
> numbers jumping between -1% and +3%, i.e. the numbers don't seem
> repeatable.  memcpy-walk sees a 70% improvement (i.e. > 2x) for 128
> bytes and that improvement reduces down as the impact of the tail copy
> decreases in comparison to the loop.
> 
> 	* sysdeps/aarch64/multiarch/memcpy_falkor.S (B_l, B_lw, C_l,
> 	D_l, E_l, F_l, G_l, A_h, B_h, C_h, D_h, E_h, F_h, G_h): New
> 	macros.
> 	(__memcpy_falkor): Use multiple registers to copy data in loop
> 	tail.

OK to commit.