On Sun, Sep 28, 2014 at 09:08:31AM -0600, Jens Axboe wrote: > On 2014-09-28 08:24, Jens Axboe wrote: > >On 2014-09-28 04:36, Sitsofe Wheeler wrote: > >>I guess I would have thought io_limit always forced wraparound. For > >>example: > >> > >># dd if=/dev/zero of=/dev/shm/1M bs=1M count=1 # fio --bs=4k > >>--filename=/dev/shm/1M --name=go1 --rw=write [...] Run status group > >>0 (all jobs): WRITE: io=1024KB, aggrb=341333KB/s, minb=341333KB/s, > >>maxb=341333KB/s, mint=3msec, maxt=3msec # fio --bs=4k > >>--filename=/dev/shm/1M --name=go2 --io_limit=2M --rw=write Run > >>status group 0 (all jobs): WRITE: io=2048KB, aggrb=341333KB/s, > >>minb=341333KB/s, maxb=341333KB/s, mint=6msec, maxt=6msec [...] # fio > >>--bs=4k --filename=/dev/shm/1M --name=go3 --io_limit=2M > >>--rw=write:4k [...] WRITE: io=512KB, aggrb=256000KB/s, > >>minb=256000KB/s, maxb=256000KB/s, mint=2msec, maxt=2msec Run status > >>group 0 (all jobs): # fio --bs=4k --filename=/dev/shm/1M --name=go4 > >>--io_limit=2M --rw=write:4k [...] Run status group 0 (all jobs): > >>WRITE: io=512KB, aggrb=256000KB/s, minb=256000KB/s, maxb=256000KB/s, > >>mint=2msec, maxt=2msec > >> > >>go2 is a plain sequential job that does twice as much I/O as go1. > >>Given that the size of the file being written to has not changed > >>between the runs one could guess that fio simply wrapped around and > >>started from the first offset (0) to write the second MB of data. > >>Given this isn't it a fair assumption that when doing a skipping > >>workload if io_limit is used (as in go4) and an offset beyond the > >>end of the device is produced the same wraparound behaviour as go2 > >>should occur and the total io done should match that specified in > >>io_limit? > > > >I would agree on that, behavior for those cases _should_ be the same. > >Without the holed IO, it closes/reopens the file and repeats the 1M > >writes. With it, it does not. I will take a look. > > Does the attached fix it up? The patch fixes fio --bs=4k --rw=write:4k --filename=/dev/shm/1M --name=go --io_limit=2M but not fio --bs=512k --rw=write --filename=/dev/shm/1M --name=go --number_io=4 or fio --bs=4k --rw=write --filename=/dev/shm/1M --name=go --zoneskip=4k --zonesize=4k --io_limit=2M -- 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
