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authorTejun Heo <tj@kernel.org>2012-02-15 09:45:53 +0100
committerJens Axboe <axboe@kernel.dk>2012-02-15 09:45:53 +0100
commit621032ad6eaabf2fe771c4fa0d8f58e1fcfcdba6 (patch)
tree903f4b1ae7dc9aa4f0538b606b1c7deb1542e704 /include/linux/iocontext.h
parent2274b029f640cd652ab59c363e5beebf5f50e609 (diff)
downloadlinux-linaro-stable-621032ad6eaabf2fe771c4fa0d8f58e1fcfcdba6.tar.gz
block: exit_io_context() should call elevator_exit_icq_fn()
While updating locking, b2efa05265 "block, cfq: unlink cfq_io_context's immediately" moved elevator_exit_icq_fn() invocation from exit_io_context() to the final ioc put. While this doesn't cause catastrophic failure, it effectively removes task exit notification to elevator and cause noticeable IO performance degradation with CFQ. On task exit, CFQ used to immediately expire the slice if it was being used by the exiting task as no more IO would be issued by the task; however, after b2efa05265, the notification is lost and disk could sit idle needlessly, leading to noticeable IO performance degradation for certain workloads. This patch renames ioc_exit_icq() to ioc_destroy_icq(), separates elevator_exit_icq_fn() invocation into ioc_exit_icq() and invokes it from exit_io_context(). ICQ_EXITED flag is added to avoid invoking the callback more than once for the same icq. Walking icq_list from ioc side and invoking elevator callback requires reverse double locking. This may be better implemented using RCU; unfortunately, using RCU isn't trivial. e.g. RCU protection would need to cover request_queue and queue_lock switch on cleanup makes grabbing queue_lock from RCU unsafe. Reverse double locking should do, at least for now. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-bisected-by: Shaohua Li <shli@kernel.org> LKML-Reference: <CANejiEVzs=pUhQSTvUppkDcc2TNZyfohBRLygW5zFmXyk5A-xQ@mail.gmail.com> Tested-by: Shaohua Li <shaohua.li@intel.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/iocontext.h')
-rw-r--r--include/linux/iocontext.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 17839c7b9614..1a3018063034 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -8,6 +8,7 @@
enum {
ICQ_IOPRIO_CHANGED = 1 << 0,
ICQ_CGROUP_CHANGED = 1 << 1,
+ ICQ_EXITED = 1 << 2,
ICQ_CHANGED_MASK = ICQ_IOPRIO_CHANGED | ICQ_CGROUP_CHANGED,
};