On Thu 14-07-11 12:30:32, Jeff Moyer wrote: > Tao Ma <tm@xxxxxx> writes: > >> - WRITE_SYNC_PLUG will plug the queue and expects explicity unplug. Who > >> is doing unplug in this case? > > See the comments I removed, "we rely on sync_buffer() doing the unplug > > for us". I removed them cause we all use pluged write now. > > Your logic is upside-down. The code currently only uses the _PLUG > variant when t_synchronous_commit is set, meaning somebody *will* call > sync_buffer. Simply setting WRITE_SYNC_PLUG doens't mean the upper > layer is going to issue the unplug. Of course, I'm not 100% sure of the > journaling process, so it may very well be that there always is an > unplug. Can Jan or someone comment on that? Anyway, you could test > this theory by seeing if your kernel generates any timer unplugs in the > blktrace output. So I'm not expert in plugging code but from what I understand when we do wait_on_buffer() (which calls io_schedule()) which will do blk_flush_plug()), the queue will get unplugged and IO starts. And we wait for all buffers we submit so we are guaranteed wait_on_buffer() will be called... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
