On Wed, Dec 09 2009, Radha Ramachandran wrote: > Hi, > The rate option currently doesnt work when used with libaio engine. > The math currently, calculates the time t2 (when the I/O completed) - > t1 (when the io_u unit was created) as the time it takes for the I/O > and the bandwidth for the rate calculation is calculated from that. > This math will work correctly for sync engine as there is only one io > in progress at a time, but for libaio engine, when there are multiple > I/Os queued, the same time (as in from t1 to t2) could be attributed > to other I/Os as well so the actual bandwidth is actually higher. > I have a patch, but this is more brute force where I take the total > bytes read/written divided by the time since I/Os started to calculate > the bandwidth and decide on the time that needs to be spent sleeping > (if any).This is a little more heavy weight than the previous math. I > think there are probably simpler/cleaner solutions than this but this > is the current patch I have for it. Good analysis, yeah it definitely is broken currently, it basically turns out to be rate*iodepth. Which is broken, of course. I have applied your patch in lieu of a better idea. Don't worry about the bit of extra math. I try to keep fio lean (and it is), the biggest problem is usually the huge amounts of gettimeofday() calls when you do high iops counts. -- 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
