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io_uring: avoid ring quiesce while registering async eventfd 

This is done using the RCU data structure (io_ev_fd). eventfd_async is
moved from io_ring_ctx to io_ev_fd which is RCU protected hence avoiding
ring quiesce which is much more expensive than an RCU lock. The place
where eventfd_async is read is already under rcu_read_lock so there is no
extra RCU read-side critical section needed.

Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Link: https://lore.kernel.org/r/20220204145117.1186568-4-usama.arif@bytedance.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Usama Arif 2022-02-04 14:51:15 +00:00 committed by Jens Axboe
parent 77bc59b498
commit c75312dd59
1 changed files with 12 additions and 10 deletions
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22
fs/io_uring.c
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@ -328,6 +328,7 @@ struct io_submit_state {
struct io_ev_fd {
struct eventfd_ctx *cq_ev_fd;
unsigned int eventfd_async: 1;
struct rcu_head rcu;
};
@ -340,7 +341,6 @@ struct io_ring_ctx {
unsigned int flags;
unsigned int compat: 1;
unsigned int drain_next: 1;
unsigned int eventfd_async: 1;
unsigned int restricted: 1;
unsigned int off_timeout_used: 1;
unsigned int drain_active: 1;
@ -1756,7 +1756,7 @@ static void io_eventfd_signal(struct io_ring_ctx *ctx)
if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
goto out;
if (!ctx->eventfd_async || io_wq_current_is_worker())
if (!ev_fd->eventfd_async || io_wq_current_is_worker())
eventfd_signal(ev_fd->cq_ev_fd, 1);
out:
@ -9385,7 +9385,8 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
return done ? done : err;
}
static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg)
static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg,
unsigned int eventfd_async)
{
struct io_ev_fd *ev_fd;
__s32 __user *fds = arg;
@ -9409,6 +9410,7 @@ static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg)
kfree(ev_fd);
return ret;
}
ev_fd->eventfd_async = eventfd_async;
rcu_assign_pointer(ctx->io_ev_fd, ev_fd);
return ret;
@ -11014,6 +11016,7 @@ static bool io_register_op_must_quiesce(int op)
case IORING_UNREGISTER_FILES:
case IORING_REGISTER_FILES_UPDATE:
case IORING_REGISTER_EVENTFD:
case IORING_REGISTER_EVENTFD_ASYNC:
case IORING_UNREGISTER_EVENTFD:
case IORING_REGISTER_PROBE:
case IORING_REGISTER_PERSONALITY:
@ -11114,17 +11117,16 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
ret = io_register_files_update(ctx, arg, nr_args);
break;
case IORING_REGISTER_EVENTFD:
ret = -EINVAL;
if (nr_args != 1)
break;
ret = io_eventfd_register(ctx, arg, 0);
break;
case IORING_REGISTER_EVENTFD_ASYNC:
ret = -EINVAL;
if (nr_args != 1)
break;
ret = io_eventfd_register(ctx, arg);
if (ret)
break;
if (opcode == IORING_REGISTER_EVENTFD_ASYNC)
ctx->eventfd_async = 1;
else
ctx->eventfd_async = 0;
ret = io_eventfd_register(ctx, arg, 1);
break;
case IORING_UNREGISTER_EVENTFD:
ret = -EINVAL;