On Thu, May 05, 2011 at 03:47:08PM +0100, David Gilbert wrote:
Hi Kiko,
On 5 May 2011 15:21, Christian Robottom Reis kiko@linaro.org wrote:
Hey there,
I was asked today in the board meeting about the use of NEON routines in the kernel; I said we had looked into this but hadn't done it because a) it wasn't conclusively better and b) if better, it would need to be done conditionally per-platform. But I wanted to double-check that's actually true (and I'm copying Vijay to keep me honest). I have some references:
Not quite: a) Neon memcpy/memset is worse on A9 than non-neon versions (better on A8 typically)
Yes. Internal hardware differences, apparently.
b) In general I don't believe fpu or Neon code can be used internally to the kernel.
Technically it *can*, but you'll then have to be responsible for dealing with all the extra register save/restores for context switches. Normal wisdom is that it's just not worth that cost unless you're doing an extended amount of such code (e.g. RAID block checksums using Neon).
Cheers,