On 5 May 2011 16:08, Måns Rullgård firstname.lastname@example.org wrote:
David Gilbert email@example.com writes:
Not quite: a) Neon memcpy/memset is worse on A9 than non-neon versions (better on A8 typically)
That is not my experience at all. On the contrary, I've seen memcpy throughput on A9 roughly double with use of NEON for large copies. For small copies, plain ARM is might be faster since the overhead of preparing for a properly aligned NEON loop is avoided.
What do you base your claims on?
at the bottom of the page are sets of graphs for A9 (left) and A8 (right); on A9 the Neon memcpy's (red and green) top out much lower than their non-neon best equivalents (black and cyan). I've seen different results for very non-aligned copies, where the vld/vst on Neon work very well.
Also, when I showed those numbers to the guys at ARM they all said it was a bad idea to use Neon on A9 for memory manipulation workloads.
What code do you base your claims on :-)
I don't see the connection between Thumb2 and memcpy performance. Thumb2 can do anything 32-bit ARM can.
There are the purists who says write everything in Thumb2 now; however there is an interesting question of which is faster, and IMHO the ARM code is likely to be a bit faster in most cases.