fio: warn about "ioengine=psync" and "iodepth >= 1"

Some users are using both ioengine=psync and iodepth=2+
without blinking in front of the millions:

	https://youtu.be/coShLkCriXc?t=840
	https://youtu.be/coShLkCriXc?t=890

Help them with helpful message.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Link: https://lore.kernel.org/r/Y0sM1PJKEzfv47ZB@localhost.localdomain
[axboe: style fixup]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/backend.c b/backend.c
index ec535bcc47955bc8bf15b64a76f43686ae5b2368..d8f4f2a508119638b212d9dc1c3481ca50e7a989 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -1791,6 +1791,11 @@ static void *thread_main(void *data)
        if (td_io_init(td))
                goto err;
 
+       if (td_ioengine_flagged(td, FIO_SYNCIO) && td->o.iodepth > 1) {
+               log_info("note: both iodepth >= 1 and synchronous I/O engine "
+                        "are selected, queue depth will be capped at 1\n");
+       }
+
        if (init_io_u(td))
                goto err;