Re: fio 3.2

[Jens Axboe <axboe@kernel.dk>]

On 11/28/2017 09:13 PM, Elliott, Robert (Persistent Memory) wrote:
> small_content_scramble has hardly been touched since 2011, so it probably
> hasn't had much performance analysis.  

That's fair, would be a good thing to look at, especially since it's on
by default.

> One of the few changes made was to add an integer divide by 1000, which 
> is always slow (painfully slow on some CPUs):
> 
> 	offset = ((io_u->start_time.tv_nsec/1000) ^ boffset) & 511;
> 
> perf top doesn't show that taking time - I think the compiler realized
> it could pull that calculation out of the loop and just do it once.  Different
> compilers and compiler options might not realize that.

Yeah, int divides suck. This didn't used to be like this, it got added
with the nsec conversion. I have fixed this up now.

-- 
Jens Axboe