io_u: tweak small content buffer scramble

[fio.git] / io_u.c

diff --git a/io_u.c b/io_u.c
index ebe82e12e8f091b02dc4dd71c708435b642dcbc1..c25854273a68d279a9265ec1780cc4fc260da4d2 100644 (file)
--- a/io_u.c
+++ b/io_u.c
@@ -1673,8 +1673,8 @@ static bool check_get_verify(struct thread_data *td, struct io_u *io_u)
 static void small_content_scramble(struct io_u *io_u)
 {
        unsigned int i, nr_blocks = io_u->buflen / 512;
-       uint64_t boffset, usec;
        unsigned int offset;
+       uint64_t boffset;
        char *p, *end;
 
        if (!nr_blocks)
@@ -1684,21 +1684,18 @@ static void small_content_scramble(struct io_u *io_u)
        boffset = io_u->offset;
        io_u->buf_filled_len = 0;
 
-       /* close enough for this purpose */
-       usec = io_u->start_time.tv_nsec >> 10;
-
        for (i = 0; i < nr_blocks; i++) {
                /*
                 * Fill the byte offset into a "random" start offset of
-                * the buffer, given by the product of the usec time
-                * and the actual offset.
+                * the first half of the buffer.
                 */
-               offset = (usec ^ boffset) & 511;
-               offset &= ~(sizeof(uint64_t) - 1);
-               if (offset >= 512 - sizeof(uint64_t))
-                       offset -= sizeof(uint64_t);
+               offset = (io_u->start_time.tv_nsec ^ boffset) & 255;
+               offset &= ~(sizeof(boffset) - 1);
                memcpy(p + offset, &boffset, sizeof(boffset));
 
+               /*
+                * Fill the start time into the end of the buffer
+                */
                end = p + 512 - sizeof(io_u->start_time);
                memcpy(end, &io_u->start_time, sizeof(io_u->start_time));
                p += 512;