> > > > Agree, however see the following sequence. > > > > __generic_make_request call q->make_request_fn(q, bio); > > It was set by blk_init_queue_node with __make_request. > > There are two ways in __make_request. > > Case 1, get_rq > > Case 2, out or merged (otherwise you mean unplug case) > > > > In case 1, if the BIO_RW_SYNC is set, the request gets the REQ_RW_SYNC > > And REQ_RW_SYNC says > > "include/linux/blkdev.h":112: __REQ_RW_SYNC, /* request is sync (O_DIRECT) */ > > It means it acts as O_DIRECT flag. Is it right? > > And it also is same as case 2. Unplug the device. > > So next time it hasn't chance to merge??? > > But that still doesn't make it sync. I think you are working the wrong > way. For ssd we still want merging and plugging also makes sense to some > degree, though it probably should be minimized. It'll only cause an > initial latency, for busy IO workloads you wont be plugging/unplugging > much anyway. > > In fact your patch makes things WORSE, since the io schedulers will now > treat the IO as sync and introduce idling for the disk head. And you > definitely don't want that. Yes, you're right. It's for testing. I just want to know the worst or corner case, if all writes are synchronous. Of course I can measure the using tiotest "Do write synchronous" option. Then you think it's the worse case? Kyungmin Park - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
