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>
diff --git a/fio.h b/fio.h
index be684ca..a5405e3 100644
--- a/fio.h
+++ b/fio.h
@@ -357,7 +357,7 @@
/*
* Rate state
*/
- unsigned long rate_nsec_cycle[2];
+ unsigned long long rate_bps[2];
long rate_pending_usleep[2];
unsigned long rate_bytes[2];
unsigned long rate_blocks[2];