io_uring: optimise mutex locking for submit+iopoll
Both submittion and iopolling requires holding uring_lock. IOPOLL can
users do them together in a single syscall, however it would still do 2
pairs of lock/unlock. Optimise this case combining locking into one
lock/unlock pair, which especially nice for low QD.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/034b6c41658648ad3ad3c9485ac8eb546f010bc4.1647957378.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5fc9779..8d3b98b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2854,12 +2854,6 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
int ret = 0;
/*
- * We disallow the app entering submit/complete with polling, but we
- * still need to lock the ring to prevent racing with polled issue
- * that got punted to a workqueue.
- */
- mutex_lock(&ctx->uring_lock);
- /*
* Don't enter poll loop if we already have events pending.
* If we do, we can potentially be spinning for commands that
* already triggered a CQE (eg in error).
@@ -2867,7 +2861,7 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
if (test_bit(0, &ctx->check_cq_overflow))
__io_cqring_overflow_flush(ctx, false);
if (io_cqring_events(ctx))
- goto out;
+ return 0;
do {
/*
* If a submit got punted to a workqueue, we can have the
@@ -2897,8 +2891,7 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
nr_events += ret;
ret = 0;
} while (nr_events < min && !need_resched());
-out:
- mutex_unlock(&ctx->uring_lock);
+
return ret;
}
@@ -10820,21 +10813,33 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
ret = io_uring_add_tctx_node(ctx);
if (unlikely(ret))
goto out;
+
mutex_lock(&ctx->uring_lock);
submitted = io_submit_sqes(ctx, to_submit);
- mutex_unlock(&ctx->uring_lock);
-
- if (submitted != to_submit)
+ if (submitted != to_submit) {
+ mutex_unlock(&ctx->uring_lock);
goto out;
+ }
+ if ((flags & IORING_ENTER_GETEVENTS) && ctx->syscall_iopoll)
+ goto iopoll_locked;
+ mutex_unlock(&ctx->uring_lock);
}
if (flags & IORING_ENTER_GETEVENTS) {
- min_complete = min(min_complete, ctx->cq_entries);
-
if (ctx->syscall_iopoll) {
+ /*
+ * We disallow the app entering submit/complete with
+ * polling, but we still need to lock the ring to
+ * prevent racing with polled issue that got punted to
+ * a workqueue.
+ */
+ mutex_lock(&ctx->uring_lock);
+iopoll_locked:
ret = io_validate_ext_arg(flags, argp, argsz);
- if (unlikely(ret))
- goto out;
- ret = io_iopoll_check(ctx, min_complete);
+ if (likely(!ret)) {
+ min_complete = min(min_complete, ctx->cq_entries);
+ ret = io_iopoll_check(ctx, min_complete);
+ }
+ mutex_unlock(&ctx->uring_lock);
} else {
const sigset_t __user *sig;
struct __kernel_timespec __user *ts;
@@ -10842,6 +10847,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
ret = io_get_ext_arg(flags, argp, &argsz, &ts, &sig);
if (unlikely(ret))
goto out;
+ min_complete = min(min_complete, ctx->cq_entries);
ret = io_cqring_wait(ctx, min_complete, sig, argsz, ts);
}
}
