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Subject[PATCH] cciss: Optimize scan_thread
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Date
Two rather small optimizations found while going through driver
code:

1) Use the cheaper alternative to set_current_state() as we are
sure the task will block right afterward.

2) Checks for list_empty without the scan_mutex. The list_empty
function is very much designed to work without locks, obviously
as long as the head (scan_q) is reliable. In this case if another
thread is doing add_to_scan_list(), we still buckle in the outer
loop, so it will be caught upon the next iteration -- and if
kthread_should_stop() hits, it does not matter _anyway_ as we'd
still need to abort the function regardless of the status of
the scan_q.

Compile tested only.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Mike Miller <mike.miller@hp.com>
Cc: Don Brace <don.brace@pmcs.com>
---
drivers/block/cciss.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index ff20f19..7dd3750 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -3727,18 +3727,13 @@ static int scan_thread(void *data)
struct ctlr_info *h;

while (1) {
- set_current_state(TASK_INTERRUPTIBLE);
+ __set_current_state(TASK_INTERRUPTIBLE);
schedule();
if (kthread_should_stop())
break;

- while (1) {
+ while (!list_empty(&scan_q)) {
mutex_lock(&scan_mutex);
- if (list_empty(&scan_q)) {
- mutex_unlock(&scan_mutex);
- break;
- }
-
h = list_entry(scan_q.next,
struct ctlr_info,
scan_list);
--
2.1.4




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