Documentation: add note about how many bssplit and zones fio supports

[fio.git] / io_u.c

diff --git a/io_u.c b/io_u.c
index 086384a1c65535dafff488440103816735fa60c8..6bb9eabf1cb281891d43cd820deb6c36b632e132 100644 (file)
--- a/io_u.c
+++ b/io_u.c
@@ -1669,32 +1669,40 @@ 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;
+       unsigned int i, nr_blocks = io_u->buflen >> 9;
        unsigned int offset;
-       uint64_t boffset;
-       char *p, *end;
+       uint64_t boffset, *iptr;
+       char *p;
 
        if (!nr_blocks)
                return;
 
        p = io_u->xfer_buf;
        boffset = io_u->offset;
-       io_u->buf_filled_len = 0;
+
+       if (io_u->buf_filled_len)
+               io_u->buf_filled_len = 0;
+
+       /*
+        * Generate random index between 0..7. We do chunks of 512b, if
+        * we assume a cacheline is 64 bytes, then we have 8 of those.
+        * Scramble content within the blocks in the same cacheline to
+        * speed things up.
+        */
+       offset = (io_u->start_time.tv_nsec ^ boffset) & 7;
 
        for (i = 0; i < nr_blocks; i++) {
                /*
-                * Fill the byte offset into a "random" start offset of
-                * the first half of the buffer.
+                * Fill offset into start of cacheline, time into end
+                * of cacheline
                 */
-               offset = (io_u->start_time.tv_nsec ^ boffset) & 255;
-               offset &= ~(sizeof(boffset) - 1);
-               memcpy(p + offset, &boffset, sizeof(boffset));
+               iptr = (void *) p + (offset << 6);
+               *iptr = boffset;
+
+               iptr = (void *) p + 64 - 2 * sizeof(uint64_t);
+               iptr[0] = io_u->start_time.tv_sec;
+               iptr[1] = io_u->start_time.tv_nsec;
 
-               /*
-                * 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;
                boffset += 512;
        }