On 04/11/2016 05:17 AM, NightStrike wrote:
> I have a routine that normally completes in just under 3 us. The
> first time through, however, it takes over 18 us. I have found that
> this is due to calling a few math library functions: tanhf, atan2f,
> hypotf, and fmod. Subsequent calls are virtually instant.
>
> I've tried putting __attribute__((optimize("prefetch-loop-arrays")))
> on the outer function, but this isn't much help (which would stand to
> reason, since it's not an issue of caching the data, but caching the
> function.) Is it at all possible to use a magic option or builtin
> that pre-caches the few library functions that I use? It's important
> for my application to reduce the gap of the first cycle time.
I'm not quite sure if I correctly understand your problem. But if you
are talking about the time it takes to resolve the math functions from
libm you might try to set the environment variable "LD_BIND_NOW" to 1
(see man ld.so). That way all external symobls get resolved at startup
(which will be slower) instead of on demand when the unresolved function
gets called.
Matthias
