Had a report on writing to eventfd with io_uring is slower than it
should be, and it's the usual case of if a file type doesn't support
->write_iter(), then io_uring cannot rely on IOCB_NOWAIT being honored
alongside O_NONBLOCK for whether or not this is a non-blocking write
attempt. That means io_uring will punt the operation to an io thread,
which will slow us down unnecessarily.
Convert eventfd to using fops->write_iter() instead of fops->write().
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
diff --git a/fs/eventfd.c b/fs/eventfd.c
index e265b6dd4f34..02c55e5e1a3e 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -264,17 +264,18 @@ static ssize_t eventfd_read(struct kiocb *iocb, struct iov_iter *to)
return sizeof(ucnt);
}
-static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
- loff_t *ppos)
+static ssize_t eventfd_write(struct kiocb *kiocb, struct iov_iter *from)
{
+ struct file *file = kiocb->ki_filp;
struct eventfd_ctx *ctx = file->private_data;
+ size_t count = iov_iter_count(from);
ssize_t res;
__u64 ucnt;
DECLARE_WAITQUEUE(wait, current);
if (count < sizeof(ucnt))
return -EINVAL;
- if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
+ if (copy_from_iter(&ucnt, count, from) != count)
return -EFAULT;
if (ucnt == ULLONG_MAX)
return -EINVAL;
@@ -282,7 +283,8 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
res = -EAGAIN;
if (ULLONG_MAX - ctx->count > ucnt)
res = sizeof(ucnt);
- else if (!(file->f_flags & O_NONBLOCK)) {
+ else if (!(file->f_flags & O_NONBLOCK) &&
+ !(kiocb->ki_flags & IOCB_NOWAIT)) {
__add_wait_queue(&ctx->wqh, &wait);
for (res = 0;;) {
set_current_state(TASK_INTERRUPTIBLE);
@@ -331,7 +333,7 @@ static const struct file_operations eventfd_fops = {
.release = eventfd_release,
.poll = eventfd_poll,
.read_iter = eventfd_read,
- .write = eventfd_write,
+ .write_iter = eventfd_write,
.llseek = noop_llseek,
};
--
Jens Axboe
