On 08/27/18 22:34, Damien Le Moal wrote: > 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 falls in > a non empty zone. The adjustment however 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 very few zones written. > > Fix this by improving the randomness of the I/Os by adjusting the I/O > offset to a random value with the range of written data in the zone. > > Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx> > --- > zbd.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/zbd.c b/zbd.c > index 56197693..a985e022 100644 > --- a/zbd.c > +++ b/zbd.c > @@ -1179,7 +1179,15 @@ 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; > + range = ((zb->wp - zb->start) << 9) - io_u->buflen; > + if (td_random(td) && range >= 0) > + io_u->offset = (zb->start << 9) + > + ((io_u->offset - (zb->start << 9)) % > + (range + 1)) / min_bs * min_bs; This looks wrong to me: it is not guaranteed that io_u->offset >= (zb->start << 9). Please use the original zb in that expression. Additionally, since that expression is only evaluated if range >=0, there is no need to add "+ 1" to "range". Thanks, Bart.
