init: add comment as to how we seed read/write/trim generators

[fio.git] / init.c

diff --git a/init.c b/init.c
index 1f1ceebf33a7d432ad29825a106c5759d0d9bcc8..9b2b63d6befc94866e8336a8a4c69bdc7e5acf06 100644 (file)
--- a/init.c
+++ b/init.c
@@ -921,6 +921,12 @@ static void td_fill_rand_seeds_internal(struct thread_data *td, bool use64)
 {
        int i;
 
+       /*
+        * trimwrite is special in that we need to generate the same
+        * offsets to get the "write after trim" effect. If we are
+        * using bssplit to set buffer length distributions, ensure that
+        * we seed the trim and write generators identically.
+        */
        if (td_trimwrite(td)) {
                init_rand_seed(&td->bsrange_state[DDIR_READ], td->rand_seeds[FIO_RAND_BS_OFF], use64);
                init_rand_seed(&td->bsrange_state[DDIR_WRITE], td->rand_seeds[FIO_RAND_BS1_OFF], use64);