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SubjectRe: [PATCH] block: strip out locking optimization in put_io_context()
On Tue, Feb 07, 2012 at 08:47:35AM -0800, Tejun Heo wrote:
> Yeah, I was about to ask Shaohua to test the version w/o optimization.
> With heavily loaded request_queue, trylock failure could be frequent,
> which I wasn't testing.
>
> Shaohua, can you please test the version w/o optimization? Also, can
> you please give a bit more details on the setup? Are there multiple
> swap devices? Is it SSD or rotating disk?

Can you please also apply the following patch on top of
block/for-linus and see how it behaves?

Thanks.
---
block/blk-ioc.c | 54 +++++++++++++++++-------------------------------------
1 file changed, 17 insertions(+), 37 deletions(-)

Index: work/block/blk-ioc.c
===================================================================
--- work.orig/block/blk-ioc.c
+++ work/block/blk-ioc.c
@@ -79,52 +79,32 @@ static void ioc_release_fn(struct work_s
{
struct io_context *ioc = container_of(work, struct io_context,
release_work);
- struct request_queue *last_q = NULL;
+ unsigned long flags;

- spin_lock_irq(&ioc->lock);
+ /*
+ * Exiting icq may call into put_io_context() through elevator
+ * which will trigger lockdep warning. The ioc's are guaranteed to
+ * be different, use a different locking subclass here. Using
+ * irqsave variant as there's no spin_lock_irq_nested().
+ */
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);

while (!hlist_empty(&ioc->icq_list)) {
struct io_cq *icq = hlist_entry(ioc->icq_list.first,
struct io_cq, ioc_node);
- struct request_queue *this_q = icq->q;
+ struct request_queue *q = icq->q;

- if (this_q != last_q) {
- /*
- * Need to switch to @this_q. Once we release
- * @ioc->lock, it can go away along with @cic.
- * Hold on to it.
- */
- __blk_get_queue(this_q);
-
- /*
- * blk_put_queue() might sleep thanks to kobject
- * idiocy. Always release both locks, put and
- * restart.
- */
- if (last_q) {
- spin_unlock(last_q->queue_lock);
- spin_unlock_irq(&ioc->lock);
- blk_put_queue(last_q);
- } else {
- spin_unlock_irq(&ioc->lock);
- }
-
- last_q = this_q;
- spin_lock_irq(this_q->queue_lock);
- spin_lock(&ioc->lock);
- continue;
+ if (spin_trylock(q->queue_lock)) {
+ ioc_exit_icq(icq);
+ spin_unlock(q->queue_lock);
+ } else {
+ spin_unlock_irqrestore(&ioc->lock, flags);
+ cpu_relax();
+ spin_lock_irqsave_nested(&ioc->lock, flags, 1);
}
- ioc_exit_icq(icq);
- }
-
- if (last_q) {
- spin_unlock(last_q->queue_lock);
- spin_unlock_irq(&ioc->lock);
- blk_put_queue(last_q);
- } else {
- spin_unlock_irq(&ioc->lock);
}

+ spin_unlock_irqrestore(&ioc->lock, flags);
kmem_cache_free(iocontext_cachep, ioc);
}


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