[patch 2/9] fio: allow general repeatability

[ehrhardt@linux.vnet.ibm.com]

*Resend with hopefully non mangled patches*
References: <20140220131958.965092001@linux.vnet.ibm.com>
Content-Disposition: inline; filename=repeatable-global-randomness.diff

From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>

This patch adds a "allrandrepeat" option similar to the existing randrepeat.
But other than the former option it does not only affect the random I/O pattern,
but also all remaining users of randomness as well.

By that e.g. testcases using nrfiles, filesize ranges, blocksizesplit ranges
and so on will stay repeatable across (euqally parametrized) runs as well.
To maintain compatibility the default is off. 

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
---

[diffstat]
 fio.1     |    8 ++++++--
 init.c    |    6 ++++++
 options.c |    7 +++++++
 3 files changed, 19 insertions(+), 2 deletions(-)


[diff]

--- a/fio.1
+++ b/fio.1
@@ -293,8 +293,12 @@ read, write, and trim are accounted and
 set, the fio will sum the results and report them as "mixed" instead.
 .TP
 .BI randrepeat \fR=\fPbool
-Seed the random number generator in a predictable way so results are repeatable
-across runs.  Default: true.
+Seed the random number generator used for random I/O patterns in a predictable
+way so the pattern is repeatable across runs.  Default: true.
+.TP
+.BI allrandrepeat \fR=\fPbool
+Seed all random number generators in a predictable way so results are
+repeatable across runs.  Default: false.
 .TP
 .BI randseed \fR=\fPint
 Seed the random number generators based on this seed value, to be able to
--- a/init.c
+++ b/init.c
@@ -751,6 +751,12 @@ static void td_fill_rand_seeds_internal(
 
 void td_fill_rand_seeds(struct thread_data *td)
 {
+	if (td->o.allrand_repeatable) {
+		for (int i = 0; i < FIO_RAND_NR_OFFS; i++)
+			td->rand_seeds[i] = FIO_RANDSEED * td->thread_number
+			       	+ i;
+	}
+
 	if (td->o.use_os_rand)
 		td_fill_rand_seeds_os(td);
 	else
--- a/options.c
+++ b/options.c
@@ -1784,6 +1784,13 @@ struct fio_option fio_options[FIO_MAX_OP
 		.group	= FIO_OPT_G_RANDOM,
 	},
 	{
+		.name	= "allrandrepeat",
+		.type	= FIO_OPT_BOOL,
+		.off1	= td_var_offset(allrand_repeatable),
+		.help	= "Use repeatable random numbers for everything",
+		.def	= "0",
+	},
+	{
 		.name	= "nrfiles",
 		.lname	= "Number of files",
 		.alias	= "nr_files",