2021-10-18 07:07:50

by Noah Goldstein

Subject: [PATCH v1] fs/io_uring: Hoist ret2 == -EAGAIN check in tail of io_write

This commit reorganizes the branches in the tail of io_write so that
the 'ret2 == -EAGAIN' check is not repeated and done first.

The previous version was duplicating the 'ret2 == -EAGAIN'. As well
'ret2 != -EAGAIN' gurantees the 'done:' path so it makes sense to
move that check to the front before the likely more expensive branches
which require memory derefences.

Signed-off-by: Noah Goldstein <[email protected]>
---
Generally I would want to rewrite this as:
```
if (ret2 != -EAGAIN
|| (req->flags & REQ_F_NOWAIT)
|| (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL)))
kiocb_done(kiocb, ret2, issue_flags);
else {
...
```

But the style of the file seems to be to use gotos. If the above is
prefereable, let me know and I'll post a new version.
fs/io_uring.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d1e672e7a2d1..932fc84d70d3 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3648,12 +3648,15 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
*/
if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
ret2 = -EAGAIN;
+
+ if (ret2 != -EAGAIN)
+ goto done;
/* no retry on NONBLOCK nor RWF_NOWAIT */
- if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
+ if (req->flags & REQ_F_NOWAIT)
goto done;
- if (!force_nonblock || ret2 != -EAGAIN) {
+ if (!force_nonblock) {
/* IOPOLL retry should happen for io-wq threads */
- if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
+ if (req->ctx->flags & IORING_SETUP_IOPOLL)
goto copy_iov;
done:
kiocb_done(kiocb, ret2, issue_flags);
--
2.29.2

2021-10-18 12:20:31

by Hao Xu

Subject: Re: [PATCH v1] fs/io_uring: Hoist ret2 == -EAGAIN check in tail of io_write

在 2021/10/18 下午3:02, Noah Goldstein 写道:
> This commit reorganizes the branches in the tail of io_write so that
> the 'ret2 == -EAGAIN' check is not repeated and done first.
>
> The previous version was duplicating the 'ret2 == -EAGAIN'. As well
> 'ret2 != -EAGAIN' gurantees the 'done:' path so it makes sense to
> move that check to the front before the likely more expensive branches
> which require memory derefences.
>
> Signed-off-by: Noah Goldstein <[email protected]>
> ---
> Generally I would want to rewrite this as:
> ```
> if (ret2 != -EAGAIN
> || (req->flags & REQ_F_NOWAIT)
> || (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL)))
> kiocb_done(kiocb, ret2, issue_flags);
> else {
> ...
> ```
To me, this one is clear enough and short, but I think better to:
if (ret2 != -EAGAIN || (req->flags & REQ_F_NOWAIT) ||
(!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))

if the first line doesn't exceed the line limit.

Reviewed-by: Hao Xu <[email protected]>
>
> But the style of the file seems to be to use gotos. If the above is
> prefereable, let me know and I'll post a new version.
> fs/io_uring.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index d1e672e7a2d1..932fc84d70d3 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3648,12 +3648,15 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
> */
> if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
> ret2 = -EAGAIN;
> +
> + if (ret2 != -EAGAIN)
> + goto done;
> /* no retry on NONBLOCK nor RWF_NOWAIT */
> - if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
> + if (req->flags & REQ_F_NOWAIT)
> goto done;
> - if (!force_nonblock || ret2 != -EAGAIN) {
> + if (!force_nonblock) {
> /* IOPOLL retry should happen for io-wq threads */
> - if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
> + if (req->ctx->flags & IORING_SETUP_IOPOLL)
> goto copy_iov;
> done:
> kiocb_done(kiocb, ret2, issue_flags);
>

2021-10-18 15:00:41

by Noah Goldstein

Subject: [PATCH v2] fs/io_uring: Hoist ret2 == -EAGAIN check in tail of io_write

This commit reorganizes the branches in the tail of io_write so that
the 'ret2 == -EAGAIN' check is not repeated and done first.

The previous version was duplicating the 'ret2 == -EAGAIN'. As well
'ret2 != -EAGAIN' gurantees the 'done:' path so it makes sense to
move that check to the front before the likely more expensive branches
which require memory derefences.

Signed-off-by: Noah Goldstein <[email protected]>
---
fs/io_uring.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d1e672e7a2d1..18293407e8bc 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3648,21 +3648,19 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
*/
if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
ret2 = -EAGAIN;
- /* no retry on NONBLOCK nor RWF_NOWAIT */
- if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
- goto done;
- if (!force_nonblock || ret2 != -EAGAIN) {
- /* IOPOLL retry should happen for io-wq threads */
- if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
- goto copy_iov;
-done:
+
+ if (ret2 != -EAGAIN ||
+ /* no retry on NONBLOCK nor RWF_NOWAIT */
+ (req->flags & REQ_F_NOWAIT)
+ /* IOPOLL retry should happen for io-wq threads */
+ || (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))) {
kiocb_done(kiocb, ret2, issue_flags);
} else {
copy_iov:
iov_iter_restore(&s->iter, &s->iter_state);
ret = io_setup_async_rw(req, iovec, s, false);
return ret ?: -EAGAIN;
- }
+}
out_free:
/* it's reportedly faster than delegating the null check to kfree() */
if (iovec)
--
2.29.2