Improve accuracy of rate= option
I noticed that the rate= option is not terribly precise in some cases.
It gets worse the higher the selected rate. For example:
$ fio -name=load -size=100g -ioengine=null -runtime=10 -rate=30m
One would expect that to read 300MB (307200KB) at close to 30MB/s
(30720KB/s). However it writes 315024KB at 31499KB/s. Further
experimentation shows that even higher rates can show bigger
discrepancies. At the extreme end...
$ fio -name=load -size=100g -ioengine=null -runtime=10 -rate=500m
One would expect this to write 5000MB at a rate of 500MB/s
(512000KB/s). However it writes close to double that (9536.8MB) at a
rate of over 953MB/s. At a rate of 1GB/s and higher, the rate
limiting is effectively ignored.
This patch improves the accuracy of the rate= option across the whole
range of rates, at the cost of being very slightly more
computationally expensive.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
3 files changed