Don't populate random data for verify reads

I was seeing some performance drop during the read verification phase
of a test, and from the code in io_u.c in get_io_u function, we
prepare/populate the buffer in the io_u structure based on the verify
patterns/options.
This makes sense when we are doing writes, but I dont understand why
we do this for the read phase when this data is going to be
overwritten anyways(and in case of truncated reads, we do modify the
buf_len).
So based on that I changed the code to populate the buffer(io_u->buf)
only if its a write with verify enabled.
This works for my tests, but I do not know if there was a reason why
this was populated for reads as well to begin with.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/io_u.c b/io_u.c
index c0beafd46ad86e8640f815792b34af0078ef4856..8c2f33b5e85e1e16bb3d6aea7564cbd5181a5e62 100644 (file)
--- a/io_u.c
+++ b/io_u.c
@@ -838,7 +838,7 @@ struct io_u *get_io_u(struct thread_data *td)
 
                f->last_pos = io_u->offset + io_u->buflen;
 
-               if (td->o.verify != VERIFY_NONE)
+               if (td->o.verify != VERIFY_NONE && io_u->ddir == DDIR_WRITE)
                        populate_verify_io_u(td, io_u);
                else if (td->o.refill_buffers && io_u->ddir == DDIR_WRITE)
                        io_u_fill_buffer(td, io_u, io_u->xfer_buflen);