iolog: run compression work at slightly elevated nice level

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index cad175c6fb59fed73407afe48ffc9cf43e6759f6..fbc455d44797dda6e779f561f1fe77178862583e 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -81,7 +81,7 @@ $ fio job_file
 and it will start doing what the job_file tells it to do. You can give
 more than one job file on the command line, fio will serialize the running
 of those files. Internally that is the same as using the 'stonewall'
-parameter described the the parameter section.
+parameter described in the parameter section.
 
 If the job file contains only one job, you may as well just give the
 parameters on the command line. The command line parameters are identical
@@ -424,10 +424,10 @@ size=int  The total size of file io for this job. Fio will run until
                Unless specific nrfiles and filesize options are given,
                fio will divide this size between the available files
                specified by the job. If not set, fio will use the full
-               size of the given files or devices. If the the files
-               do not exist, size must be given. It is also possible to
-               give size as a percentage between 1 and 100. If size=20%
-               is given, fio will use 20% of the full size of the given
+               size of the given files or devices. If the files do not
+               exist, size must be given. It is also possible to give
+               size as a percentage between 1 and 100. If size=20% is
+               given, fio will use 20% of the full size of the given
                files or devices.
 
 io_limit=int   Normally fio operates within the region set by 'size', which
@@ -1333,6 +1333,29 @@ log_avg_msec=int By default, fio will log an entry in the iops, latency,
                specified period of time, reducing the resolution of the log.
                Defaults to 0.
 
+log_offset=int If this is set, the iolog options will include the byte
+               offset for the IO entry as well as the other data values.
+
+log_compression=int    If this is set, fio will compress the IO logs as
+               it goes, to keep the memory footprint lower. When a log
+               reaches the specified size, that chunk is removed and
+               compressed in the background. Given that IO logs are
+               fairly highly compressible, this yields a nice memory
+               savings for longer runs. The downside is that the
+               compression will consume some background CPU cycles, so
+               it may impact the run. This, however, is also true if
+               the logging ends up consuming most of the system memory.
+               So pick your poison. The IO logs are saved normally at the
+               end of a run, by decompressing the chunks and storing them
+               in the specified log file. This feature depends on the
+               availability of zlib.
+
+log_store_compressed=bool      If set, and log_compression is also set,
+               fio will store the log files in a compressed format. They
+               can be decompressed with fio, using the --inflate-log
+               command line parameter. The files will be stored with a
+               .fz suffix.
+
 lockmem=int    Pin down the specified amount of memory with mlock(2). Can
                potentially be used instead of removing memory or booting
                with less memory to simulate a smaller amount of memory.