Don't overwrite error

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 95d059e766e6399f29d8097331a076db4df29161..237b3ad23879efea84dbe46c69bd6754dc932f1d 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -49,7 +49,7 @@ bottom, it contains the following basic parameters:
 
        IO engine       How do we issue io? We could be memory mapping the
                        file, we could be using regular read/write, we
 
        IO engine       How do we issue io? We could be memory mapping the
                        file, we could be using regular read/write, we

-                       could be using splice, async io, or even
+                       could be using splice, async io, syslet, or even

                        SG (SCSI generic sg).
 
        IO depth        If the io engine is async, how large a queuing
                        SG (SCSI generic sg).
 
        IO depth        If the io engine is async, how large a queuing


@@ -108,8 +108,8 @@ to use any ascii name you want, except 'global' which has special meaning.
 A global section sets defaults for the jobs described in that file. A job
 may override a global section parameter, and a job file may even have
 several global sections if so desired. A job is only affected by a global
 A global section sets defaults for the jobs described in that file. A job
 may override a global section parameter, and a job file may even have
 several global sections if so desired. A job is only affected by a global

-section residing above it. If the first character in a line is a ';', the
-entire line is discarded as a comment.
+section residing above it. If the first character in a line is a ';' or a
+'#', the entire line is discarded as a comment.

 
 So lets look at a really simple job file that define to threads, each
 randomly reading from a 128MiB file.
 
 So lets look at a really simple job file that define to threads, each
 randomly reading from a 128MiB file.


@@ -193,13 +193,19 @@ name=str  ASCII name of the job. This may be used to override the
                special purpose of also signaling the start of a new
                job.
 
                special purpose of also signaling the start of a new
                job.
 

+description=str        Text description of the job. Doesn't do anything except
+               dump this text description when this job is run. It's
+               not parsed.
+

 directory=str  Prefix filenames with this directory. Used to places files
                in a different location than "./".
 
 filename=str   Fio normally makes up a filename based on the job name,
                thread number, and file number. If you want to share
                files between threads in a job or several jobs, specify
 directory=str  Prefix filenames with this directory. Used to places files
                in a different location than "./".
 
 filename=str   Fio normally makes up a filename based on the job name,
                thread number, and file number. If you want to share
                files between threads in a job or several jobs, specify

-               a filename for each of them to override the default.
+               a filename for each of them to override the default. If
+               the ioengine used is 'net', the filename is the host and
+               port to connect to in the format of =host:port.

 
 rw=str         Type of io pattern. Accepted values are:
 
 
 rw=str         Type of io pattern. Accepted values are:
 


@@ -264,6 +270,9 @@ ioengine=str        Defines how the job issues io to the file. The following
                                vmsplice(2) to transfer data from user
                                space to the kernel.
 
                                vmsplice(2) to transfer data from user
                                space to the kernel.
 

+                       syslet-rw Use the syslet system calls to make
+                               regular read/write async.
+

                        sg      SCSI generic sg v3 io. May either be
                                synchronous using the SG_IO ioctl, or if
                                the target is an sg character device
                        sg      SCSI generic sg v3 io. May either be
                                synchronous using the SG_IO ioctl, or if
                                the target is an sg character device


@@ -274,11 +283,24 @@ ioengine=str      Defines how the job issues io to the file. The following
                                to. This is mainly used to exercise fio
                                itself and for debugging/testing purposes.
 
                                to. This is mainly used to exercise fio
                                itself and for debugging/testing purposes.
 

+                       net     Transfer over the network to given host:port.
+                               'filename' must be set appropriately to
+                               filename=host:port regardless of send
+                               or receive, if the latter only the port
+                               argument is used.
+

 iodepth=int    This defines how many io units to keep in flight against
                the file. The default is 1 for each file defined in this
                job, can be overridden with a larger value for higher
                concurrency.
 
 iodepth=int    This defines how many io units to keep in flight against
                the file. The default is 1 for each file defined in this
                job, can be overridden with a larger value for higher
                concurrency.
 

+iodepth_low=int        The low water mark indicating when to start filling
+               the queue again. Defaults to the same as iodepth, meaning
+               that fio will attempt to keep the queue full at all times.
+               If iodepth is set to eg 16 and iodepth_low is set to 4, then
+               after fio has filled the queue of 16 requests, it will let
+               the depth drain down to 4 before starting to fill it again.
+

 direct=bool    If value is true, use non-buffered io. This is usually
                O_DIRECT.
 
 direct=bool    If value is true, use non-buffered io. This is usually
                O_DIRECT.
 


@@ -328,7 +350,14 @@ prioclass=int      Set the io priority class. See man ionice(1).
 
 thinktime=int  Stall the job x microseconds after an io has completed before
                issuing the next. May be used to simulate processing being
 
 thinktime=int  Stall the job x microseconds after an io has completed before
                issuing the next. May be used to simulate processing being

-               done by an application. See thinktime_blocks.
+               done by an application. See thinktime_blocks and
+               thinktime_spin.
+
+thinktime_spin=int
+               Only valid if thinktime is set - pretend to spend CPU time
+               doing something with the data received, before falling back
+               to sleeping for the rest of the period specified by
+               thinktime.

 
 thinktime_blocks
                Only valid if thinktime is set - control how many blocks
 
 thinktime_blocks
                Only valid if thinktime is set - control how many blocks


@@ -423,8 +452,9 @@ create_serialize=bool       If true, serialize the file creating for the jobs.
 create_fsync=bool      fsync the data file after creation. This is the
                        default.
 
 create_fsync=bool      fsync the data file after creation. This is the
                        default.
 

-unlink=bool    Unlink the job files when done. fio defaults to doing this,
-               if it created the file itself.
+unlink=bool    Unlink the job files when done. Not the default, as repeated
+               runs of that job would then waste time recreating the fileset
+               again and again.

 
 loops=int      Run the specified number of iterations of this job. Used
                to repeat the same workload a given number of times. Defaults
 
 loops=int      Run the specified number of iterations of this job. Used
                to repeat the same workload a given number of times. Defaults


@@ -540,6 +570,8 @@ Client1 (g=0): err= 0:
     bw (KiB/s) : min=    0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
   cpu        : usr=1.49%, sys=0.25%, ctx=7969
   IO depths    : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
     bw (KiB/s) : min=    0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
   cpu        : usr=1.49%, sys=0.25%, ctx=7969
   IO depths    : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%

+     lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
+     lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%

 
 The client number is printed, along with the group id and error of that
 thread. Below is the io statistics, here for writes. In the order listed,
 
 The client number is printed, along with the group id and error of that
 thread. Below is the io statistics, here for writes. In the order listed,


@@ -569,6 +601,12 @@ IO depths= The distribution of io depths over the job life time. The
                16= entries includes depths up to that value but higher
                than the previous entry. In other words, it covers the
                range from 16 to 31.
                16= entries includes depths up to that value but higher
                than the previous entry. In other words, it covers the
                range from 16 to 31.

+IO latencies=  The distribution of IO completion latencies. This is the
+               time from when IO leaves fio and when it gets completed.
+               The numbers follow the same pattern as the IO depths,
+               meaning that 2=1.6% means that 1.6% of the IO completed
+               within 2 msecs, 20=12.8% means that 12.8% of the IO
+               took more than 10 msecs, but less than (or equal to) 20 msecs.

 
 After each client has been listed, the group statistics are printed. They
 will look like this:
 
 After each client has been listed, the group statistics are printed. They
 will look like this: