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 -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
