public inbox for [email protected]
 help / color / mirror / Atom feed
From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>, Andres Freund <[email protected]>
Cc: [email protected]
Subject: Re: Deduplicate io_*_prep calls?
Date: Mon, 24 Feb 2020 19:18:26 +0300	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>


[-- Attachment #1.1: Type: text/plain, Size: 1721 bytes --]

On 24/02/2020 19:02, Jens Axboe wrote:
>> Usually doesn't work because of such possible "hackier assignments".
>> Ok, I have to go and experiment a bit. Anyway, it probably generates a lot of
>> useless stuff, e.g. for req->ctx
> 
> Tried this, and it generates the same code...

Maybe it wasn't able to optimise in the first place

E.g. for the following code any compiler generates 2 reads (thanks godbolt).

extern void foo(int);
int bar(const int *v)
{
    foo(*v);
    return *v;
}

> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index ba8d4e2d9f99..8de5863aa749 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -598,7 +598,7 @@ struct io_kiocb {
>  
>  	struct io_async_ctx		*io;
>  	bool				needs_fixed_file;
> -	u8				opcode;
> +	const u8			opcode;
>  
>  	struct io_ring_ctx	*ctx;
>  	struct list_head	list;
> @@ -5427,6 +5427,8 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct io_kiocb *req,
>  	 */
>  	head = READ_ONCE(sq_array[ctx->cached_sq_head & ctx->sq_mask]);
>  	if (likely(head < ctx->sq_entries)) {
> +		u8 *op;
> +
>  		/*
>  		 * All io need record the previous position, if LINK vs DARIN,
>  		 * it can be used to mark the position of the first IO in the
> @@ -5434,7 +5436,8 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct io_kiocb *req,
>  		 */
>  		req->sequence = ctx->cached_sq_head;
>  		*sqe_ptr = &ctx->sq_sqes[head];
> -		req->opcode = READ_ONCE((*sqe_ptr)->opcode);
> +		op = (void *) req + offsetof(struct io_kiocb, opcode);
> +		*op = READ_ONCE((*sqe_ptr)->opcode);
>  		req->user_data = READ_ONCE((*sqe_ptr)->user_data);
>  		ctx->cached_sq_head++;
>  		return true;
> 

-- 
Pavel Begunkov


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

  reply	other threads:[~2020-02-24 16:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-24  1:07 Deduplicate io_*_prep calls? Andres Freund
2020-02-24  3:17 ` Jens Axboe
2020-02-24  3:33   ` Andres Freund
2020-02-24  3:52     ` Jens Axboe
2020-02-24  7:12       ` Andres Freund
2020-02-24  9:10         ` Pavel Begunkov
2020-02-24 15:40         ` Jens Axboe
2020-02-24 15:44           ` Pavel Begunkov
2020-02-24 15:46             ` Jens Axboe
2020-02-24 15:50               ` Pavel Begunkov
2020-02-24 15:53                 ` Jens Axboe
2020-02-24 15:56                   ` Pavel Begunkov
2020-02-24 16:02                     ` Jens Axboe
2020-02-24 16:18                       ` Pavel Begunkov [this message]
2020-02-24 17:08                         ` Andres Freund
2020-02-24 17:16                           ` Pavel Begunkov
2020-02-25  9:26                 ` Pavel Begunkov
2020-02-27 21:06                   ` Andres Freund
2020-02-24 16:53           ` Andres Freund
2020-02-24 17:19             ` Jens Axboe
2020-02-24 17:30               ` Jens Axboe
2020-02-24 17:37               ` Pavel Begunkov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox