Improve rate limiting

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 1390f386adca52a4c4ccdec3d60c6c730b9392e5..536e370ba03f0c5f3c9d3d8fc03ddd559c0cc95b 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -314,7 +314,8 @@ filesize=int        Individual file sizes. May be a range, in which case fio
 
 fill_device=bool Sets size to something really large and waits for ENOSPC (no
                space left on device) as the terminating condition. Only makes
-                sense with sequential write.
+                sense with sequential write. For a read workload, the mount
+               point will be filled first then IO started on the result.
 
 blocksize=int
 bs=int         The block size used for the io units. Defaults to 4k. Values
@@ -546,7 +547,9 @@ rwmixread=int       How large a percentage of the mix should be reads.
 rwmixwrite=int How large a percentage of the mix should be writes. If both
                rwmixread and rwmixwrite is given and the values do not add
                up to 100%, the latter of the two will be used to override
-               the first.
+               the first. This may interfere with a given rate setting,
+               if fio is asked to limit reads or writes to a certain rate.
+               If that is the case, then the distribution may be skewed.
 
 norandommap    Normally fio will cover every block of the file when doing
                random IO. If this option is given, fio will just get a
@@ -588,19 +591,29 @@ thinktime_blocks
                defaults to 1 which will make fio wait 'thinktime' usecs
                after every block.
 
-rate=int       Cap the bandwidth used by this job to this number of KiB/sec.
+rate=int       Cap the bandwidth used by this job. The number is in bytes/sec,
+               the normal postfix rules apply. You can use rate=500k to limit
+               reads and writes to 500k each, or you can specify read and
+               writes separately. Using rate=1m,500k would limit reads to
+               1MB/sec and writes to 500KB/sec. Capping only reads or
+               writes can be done with rate=,500k or rate=500k,. The former
+               will only limit writes (to 500KB/sec), the latter will only
+               limit reads.
 
 ratemin=int    Tell fio to do whatever it can to maintain at least this
                bandwidth. Failing to meet this requirement, will cause
-               the job to exit.
+               the job to exit. The same format as rate is used for
+               read vs write separation.
 
 rate_iops=int  Cap the bandwidth to this number of IOPS. Basically the same
                as rate, just specified independently of bandwidth. If the
                job is given a block size range instead of a fixed value,
-               the smallest block size is used as the metric.
+               the smallest block size is used as the metric. The same format
+               as rate is used for read vs write seperation.
 
 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
-               the job to exit.
+               the job to exit. The same format as rate is used for read vs
+               write seperation.
 
 ratecycle=int  Average bandwidth for 'rate' and 'ratemin' over this number
                of milliseconds.
@@ -714,7 +727,9 @@ create_on_open=bool Don't pre-setup the files for IO, just create open()
                        when it's time to do IO to that file.
 
 pre_read=bool  If this is given, files will be pre-read into memory before
-               starting the given IO operation.
+               starting the given IO operation. This will also clear
+               the 'invalidate' flag, since it is pointless to pre-read
+               and then drop the cache.
 
 unlink=bool    Unlink the job files when done. Not the default, as repeated
                runs of that job would then waste time recreating the file
@@ -931,6 +946,7 @@ Idle        Run
 P              Thread setup, but not started.
 C              Thread created.
 I              Thread initialized, waiting.
+       p       Thread running pre-reading file(s).
        R       Running, doing sequential reads.
        r       Running, doing random reads.
        W       Running, doing sequential writes.