Tejun Heo notes:
"I'm currently debugging this. The problem is that we are using the
generic dispatch queue directly in the noop sched and merging is NOT
allowed on dispatch queues but generic handling of last_merge tries
to merge requests. I'm still trying to verify this, so I'll be back
with results soon."
In the meantime, disable merging for noop by setting REQ_NOMERGE in
elevator_noop_add_request().
Eventually, we should add a noop_list and do the dispatching like in the
other io schedulers. Merging is still beneficial for noop (and it has
always done it).
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This patch updates all four ioscheds to use generic dispatch
queue. There's one behavior change in as-iosched.
* In as-iosched, when force dispatching
(ELEVATOR_INSERT_BACK), batch_data_dir is reset to REQ_SYNC
and changed_batch and new_batch are cleared to zero. This
prevernts AS from doing incorrect update_write_batch after
the forced dispatched requests are finished.
* In cfq-iosched, cfqd->rq_in_driver currently counts the
number of activated (removed) requests to determine
whether queue-kicking is needed and cfq_max_depth has been
reached. With generic dispatch queue, I think counting
the number of dispatched requests would be more appropriate.
* cfq_max_depth can be lowered to 1 again.
Original from Tejun Heo, modified version applied.
Signed-off-by: Jens Axboe <axboe@suse.de>
Profiling hit rates on merging shows that the last merge hint works
extremely well for most work loads. So lets kill the linear merge scan in
noop-iosched, so it provides O(1) run time for any operation.
Testing credits go to Ken Chen from Intel.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Jens Axboe