> Il giorno 27 mag 2018, alle ore 16:24, Sitsofe Wheeler <sitsofe@xxxxxxxxx> ha scritto: > > Hi Paolo! > > On 25 May 2018 at 20:20, Paolo Valente <paolo.valente@xxxxxxxxxx> wrote: >> Hi, >> if I run this job (even with the last version GitHub version of fio) on an SSD: >> [global] >> ioengine=sync >> time_based=1 >> runtime=20 >> readwrite=randread >> size=100m >> numjobs=1 >> invalidate=1 >> [job1] >> >> then, after little time (I think after 100MB have been read), fio reports a nonsensically large value for the throughput, while a simple iostat shows that no I/O is going on. By just replacing time_based with loops, i.e., with a job file like this: >> >> [global] >> ioengine=sync >> loops=1000 >> readwrite=randread >> size=100m >> numjobs=1 >> invalidate=1 >> [job1] >> >> the problem disappears. > > I've taken a stab at fixing this over in > https://github.com/sitsofe/fio/tree/random_reinvalidate - does that > solve the issue for you too? Nope :( > ... > I know I'm "Teaching grandmother to suck eggs" given that you're the > author of BFQ but just in case... > > This issue happens on loops=1000 too and I believe it's down to > readahead. I'm afraid there is a misunderstanding on this, grandson :) As I wrote, this problem does not occur with loops=1000. My impression is that, with loops, as well as with time-based and read, fio does invalidate the cache every time it restarts reading the same file, while with time_based and randread it does not (or maybe it tries to, but fails for some reason). Thanks, grandma > Basically fio is trying to invalidate the cache but said > cache is also being populated by readahead and in the end some data > ends up reused from the cache: > > # modprobe null_blk completion_nsec=100000 irqmode=2 > # > # ./fio --ioengine=sync --runtime=10 --size=100m > --filename=/dev/nullb0 --time_based --name=cached --rw=read --stats=0 > --invalidate=1 > cached: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=sync, iodepth=1 > fio-3.6-40-g854d > Starting 1 process > Jobs: 1 (f=1): [R(1)][100.0%][r=2233MiB/s,w=0KiB/s][r=572k,w=0 > IOPS][eta 00m:00s] > > Run status group 0 (all jobs): > > Disk stats (read/write): > nullb0: ios=266158/0, merge=0/0, ticks=26611/0, in_queue=26492, util=82.39% > # ./fio --ioengine=sync --runtime=10 --size=100m > --filename=/dev/nullb0 --time_based --name=cached --rw=read --stats=0 > --invalidate=1 --fadvise=random > cached: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=sync, iodepth=1 > fio-3.6-40-g854d > Starting 1 process > Jobs: 1 (f=1): [R(1)][100.0%][r=37.3MiB/s,w=0KiB/s][r=9561,w=0 > IOPS][eta 00m:00s] > > Run status group 0 (all jobs): > > Disk stats (read/write): > nullb0: ios=94364/0, merge=0/0, ticks=9615/0, in_queue=9612, util=96.15% > # ./fio --ioengine=sync --runtime=10 --size=100m > --filename=/dev/nullb0 --time_based --name=cached --rw=read --stats=0 > --invalidate=0 > cached: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=sync, iodepth=1 > fio-3.6-40-g854d > Starting 1 process > Jobs: 1 (f=1): [R(1)][100.0%][r=3888MiB/s,w=0KiB/s][r=995k,w=0 > IOPS][eta 00m:00s] > > Run status group 0 (all jobs): > > Disk stats (read/write): > nullb0: ios=1208/0, merge=0/0, ticks=122/0, in_queue=121, util=0.37% > # > # echo 0 > /sys/block/nullb0/queue/read_ahead_kb > # > # ./fio --ioengine=sync --runtime=10 --size=100m > --filename=/dev/nullb0 --time_based --name=cached --rw=read --stats=0 > --invalidate=1 > cached: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=sync, iodepth=1 > fio-3.6-40-g854d > Starting 1 process > Jobs: 1 (f=1): [R(1)][100.0%][r=37.0MiB/s,w=0KiB/s][r=9478,w=0 > IOPS][eta 00m:00s] > > Run status group 0 (all jobs): > > Disk stats (read/write): > nullb0: ios=93518/0, merge=0/0, ticks=9654/0, in_queue=9653, util=96.56% > # ./fio --ioengine=sync --runtime=10 --size=100m > --filename=/dev/nullb0 --time_based --name=cached --rw=read --stats=0 > --invalidate=0 > cached: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=sync, iodepth=1 > fio-3.6-40-g854d > Starting 1 process > Jobs: 1 (f=1): [R(1)][100.0%][r=3894MiB/s,w=0KiB/s][r=997k,w=0 > IOPS][eta 00m:00s] > > Run status group 0 (all jobs): > > Disk stats (read/write): > nullb0: ios=25600/0, merge=0/0, ticks=2650/0, in_queue=2649, util=26.50% > > Note: readahead (if set) can still take place even when the > ioscheduler has been set to none. > > -- > Sitsofe | http://sucs.org/~sits/ -- 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
