* Jens Axboe <axboe@xxxxxxxxx> [130925 14:05]: > > Hi, > > > > I'm still a bit puzzled about the amount of data read by > > individual processes spawned by fio. Given the following (now > > simplified) job file: > > > > --- snip --- > > [global] > > ioengine=sync > > direct=0 > > bssplit=19k/25:177k/15:350k/60 > > size=100m > > numjobs=4 > > directory=/tmp > > > > [work] > > rw=randread > > --- snip --- > > > > $ fio jobfile.fio >fio.out > > $ grep io= fio.out > > read : io=199968KB, bw=4892.6KB/s, iops=27, runt= 40872msec > > read : io=200062KB, bw=5083.5KB/s, iops=28, runt= 39359msec > > read : io=200156KB, bw=4989.1KB/s, iops=27, runt= 40112msec > > read : io=199940KB, bw=4492.4KB/s, iops=24, runt= 44507msec > > READ: io=800126KB, aggrb=17977KB/s, minb=4492KB/s, maxb=5083KB/s, mint=39359msec, maxt=44507msec > > > > I.e. every individual process reads approx. 200 MB of data rather > > than 100 MB as specified in the job file. For sequential reads > > (i.e. replaced rw=randread by rw=read, but otherwise unchanged job > > file) the amount of data read by each process is close to 100 MB as > > expected. > > > > I am probably missing something obvious, but why does the job file > > above result in 200 MB read by every process? > > It should not, that's definitely a bug. I'm guessing it's triggered by > the strange block sizes being used. Can you see if adding: > > random_generator=lfsr > > helps? Thanks for your response, Jens. Yes it does. It's a bit confusing though, as the man page says "LFSR only works with single block sizes, not with workloads that use multiple block sizes. If used with such a workload, fio may read or write some blocks multiple times." Shouldn't this be read as "Don't use LFSR with mixed block sizes."? I am sorry to keep on harping on the matter, but I am planning to use fio for simulating file sizes where total runtime will become a serious issue. And these simulations will definitely involve strange mixed block sizes ... Thanks again. Best regards, Juergen -- 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
