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Subject[PATCH 4/4] aio: allow direct aio poll comletions for keyed wakeups
Date
If we get a keyed wakeup for a aio poll waitqueue and wake can acquire the
ctx_lock without spinning we can just complete the iocb straight from the
wakeup callback to avoid a context switch.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Avi Kivity <avi@scylladb.com>
---
fs/aio.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 2fd19521d8a8..29f2b5b57d32 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1672,13 +1672,26 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
void *key)
{
struct poll_iocb *req = container_of(wait, struct poll_iocb, wait);
+ struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);
__poll_t mask = key_to_poll(key);

req->woken = true;

/* for instances that support it check for an event match first: */
- if (mask && !(mask & req->events))
- return 0;
+ if (mask) {
+ if (!(mask & req->events))
+ return 0;
+
+ /* try to complete the iocb inline if we can: */
+ if (spin_trylock(&iocb->ki_ctx->ctx_lock)) {
+ list_del(&iocb->ki_list);
+ spin_unlock(&iocb->ki_ctx->ctx_lock);
+
+ list_del_init(&req->wait.entry);
+ aio_poll_complete(iocb, mask);
+ return 1;
+ }
+ }

list_del_init(&req->wait.entry);
schedule_work(&req->work);
--
2.18.0
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