With zonemode=zbd, for random read operations with read_beyond_wp=0,
the zbd code will always adjust an I/O offset so that the I/O hits a
non empty zone. However, the adjustment always sets the I/O offset to
the start of the zone, resulting in a high device read cache hit rate
if the device has few zones written.
Improve randomness of read I/Os by adjusting the I/O offset to a random
value within the range of written data of the chosen zone. Also ensure
that the modified I/O does not cross over the zone wp position by
adjusting its size. Doing so, the search for a new zone is now done only
if the target zone cannot accomodate an I/O of at least min_bs bytes.
The comments have also been changed to better explain the code.
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
zbd.c | 59 +++++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 39 insertions(+), 20 deletions(-)
diff --git a/zbd.c b/zbd.c
index 56197693..93f14410 100644
--- a/zbd.c
+++ b/zbd.c
@@ -1119,7 +1119,7 @@ enum io_u_action zbd_adjust_block(struct thread_data *td, struct io_u *io_u)
{
const struct fio_file *f = io_u->file;
uint32_t zone_idx_b;
- struct fio_zone_info *zb, *zl;
+ struct fio_zone_info *zb, *zl, *orig_zb;
uint32_t orig_len = io_u->buflen;
uint32_t min_bs = td->o.min_bs[io_u->ddir];
uint64_t new_len;
@@ -1132,6 +1132,7 @@ enum io_u_action zbd_adjust_block(struct thread_data *td, struct io_u *io_u)
assert(io_u->buflen);
zone_idx_b = zbd_zone_idx(f, io_u->offset);
zb = &f->zbd_info->zone_info[zone_idx_b];
+ orig_zb = zb;
/* Accept the I/O offset for conventional zones. */
if (zb->type == BLK_ZONE_TYPE_CONVENTIONAL)
@@ -1153,21 +1154,14 @@ enum io_u_action zbd_adjust_block(struct thread_data *td, struct io_u *io_u)
goto accept;
}
/*
- * Avoid reads past the write pointer because such reads do not
- * hit the medium.
+ * Check that there is enough written data in the zone to do an
+ * I/O of at least min_bs B. If there isn't, find a new zone for
+ * the I/O.
*/
range = zb->cond != BLK_ZONE_COND_OFFLINE ?
- ((zb->wp - zb->start) << 9) - io_u->buflen : 0;
- if (td_random(td) && range >= 0) {
- io_u->offset = (zb->start << 9) +
- ((io_u->offset - (zb->start << 9)) %
- (range + 1)) / min_bs * min_bs;
- assert(zb->start << 9 <= io_u->offset);
- assert(io_u->offset + io_u->buflen <= zb->wp << 9);
- goto accept;
- }
- if (zb->cond == BLK_ZONE_COND_OFFLINE ||
- (io_u->offset + io_u->buflen) >> 9 > zb->wp) {
+ (zb->wp - zb->start) << 9 : 0;
+ if (range < min_bs ||
+ ((!td_random(td)) && (io_u->offset + min_bs > zb->wp << 9))) {
pthread_mutex_unlock(&zb->mutex);
zl = &f->zbd_info->zone_info[zbd_zone_idx(f,
f->file_offset + f->io_size)];
@@ -1179,14 +1173,39 @@ enum io_u_action zbd_adjust_block(struct thread_data *td, struct io_u *io_u)
io_u->buflen);
goto eof;
}
- io_u->offset = zb->start << 9;
+ /*
+ * zbd_find_zone() returned a zone with a range of at
+ * least min_bs.
+ */
+ range = (zb->wp - zb->start) << 9;
+ assert(range >= min_bs);
+
+ if (!td_random(td))
+ io_u->offset = zb->start << 9;
}
- if ((io_u->offset + io_u->buflen) >> 9 > zb->wp) {
- dprint(FD_ZBD, "%s: %lld + %lld > %" PRIu64 "\n",
- f->file_name, io_u->offset, io_u->buflen,
- zb->wp);
- goto eof;
+ /*
+ * Make sure the I/O is within the zone valid data range while
+ * maximizing the I/O size and preserving randomness.
+ */
+ if (range <= io_u->buflen)
+ io_u->offset = zb->start << 9;
+ else if (td_random(td))
+ io_u->offset = (zb->start << 9) +
+ ((io_u->offset - (orig_zb->start << 9)) %
+ (range - io_u->buflen)) / min_bs * min_bs;
+ /*
+ * Make sure the I/O does not cross over the zone wp position.
+ */
+ new_len = min((unsigned long long)io_u->buflen,
+ (unsigned long long)(zb->wp << 9) - io_u->offset);
+ new_len = new_len / min_bs * min_bs;
+ if (new_len < io_u->buflen) {
+ io_u->buflen = new_len;
+ dprint(FD_IO, "Changed length from %u into %llu\n",
+ orig_len, io_u->buflen);
}
+ assert(zb->start << 9 <= io_u->offset);
+ assert(io_u->offset + io_u->buflen <= zb->wp << 9);
goto accept;
case DDIR_WRITE:
if (io_u->buflen > (f->zbd_info->zone_size << 9))
--
2.17.1
