AIO: Don't plug the I/O queue in do_io_submit()

Asynchronous I/O latency to a solid-state disk greatly increased
between the 2.6.32 and 3.0 kernels. By removing the plug from
do_io_submit(), we observed a 34% improvement in the I/O latency.

Unfortunately, at this level, we don't know if the request is to
a rotating disk or not.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: linux-aio@kvack.org
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Revert "This is a more stocky test, this might very well be gone again soon."

This reverts commit d79e7bbc55c60f27cb81068277264f601344a657.
Revert "rcu: Stop rcu_do_batch() from multiplexing the "count" variable"

This reverts commit ede3a9bcfee69c909bf39111a223c2ec54e080b0.
Revert "Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation""

This reverts commit 24f008570abac97b88c5dc28b524f7ff0a943638.
Revert "rcu: Precompute RCU_FAST_NO_HZ timer offsets"

This reverts commit 9e9c1ff303bc76572fc70acff1bff1ca22bb35b9.
Revert "rcu: Move RCU_FAST_NO_HZ per-CPU variables to rcu_dynticks structure"

This reverts commit 677936cd314c03130d2e245270dec0a30ded19ed.
Revert "rcu: Update RCU_FAST_NO_HZ tracing for lazy callbacks"

This reverts commit 2364c8660ff2b9a0b78cba1f347c58bb60918bf5.
Revert "timer: Fix mod_timer_pinned() header comment"

This reverts commit 6a45f46f1f77a284afcda291d37789cd9b08b24b.
Revert "rcu: Make rcu_barrier() less disruptive"

This reverts commit 1cfec835ada6ed87363c2092bd032844c2c05b7a.
Revert "rcu: Explicitly initialize RCU_FAST_NO_HZ per-CPU variables"

This reverts commit ff5d9bb394429c32a6ab493820181698c2796947.
Revert "rcu: Make RCU_FAST_NO_HZ handle timer migration"

This reverts commit 99dbc2edd394f3cbd68ae6509d48ad5a808c5efa.
Revert "rcu: Make exit_rcu() more precise and consolidate"

This reverts commit 73bbc40fbe06968c55328fa765282204f524ab99.
Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"

This reverts commit daf6b9b1f045260a00ff441563fc5d25ab93ac24.
Revert "rcu: Ensure that RCU_FAST_NO_HZ timers expire on correct CPU"

This reverts commit ca083dc19f4aa67f8ab76e7467dbc6ac025399f8.
Revert "rcu: Add warning for RCU_FAST_NO_HZ timer firing"

This reverts commit de3bf4adf3dd6416ee3cbbe979d3a75a28ad7f41.
Revert "rcu: Make RCU_FAST_NO_HZ account for pauses out of idle"

This reverts commit 346fd6fb5f5d4c52a0765885ff3177ff7aee5e95.
Revert "rcu: Make RCU_FAST_NO_HZ use timer rather than hrtimer"

This reverts commit 6406d394d1e4d82863870709ed91ef487a9d02a7.
Revert "rcu: Add RCU_FAST_NO_HZ tracing for idle exit"

This reverts commit 12d03ec6f4683a9b389689da08bd45b87246bcab.