linux-kernel - Re: [PATCH] io_uring: Use atomic_long_try_cmpxchg in __io_account

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Message-ID: <2ca14dec-6e87-2e9a-80f7-0790f6e1f7cf@kernel.dk>
Date:   Thu, 14 Jul 2022 10:45:04 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Uros Bizjak <ubizjak@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH] io_uring: Use atomic_long_try_cmpxchg in __io_account_mem

On 7/14/22 10:33 AM, Uros Bizjak wrote:
> Use atomic_long_try_cmpxchg instead of
> atomic_long_cmpxchg (*ptr, old, new) == old in __io_account_mem.
> x86 CMPXCHG instruction returns success in ZF flag, so this
> change saves a compare after cmpxchg (and related move
> instruction in front of cmpxchg).
> 
> Also, atomic_long_try_cmpxchg implicitly assigns old *ptr value
> to "old" when cmpxchg fails, enabling further code simplifications.
> 
> No functional change intended.

This will be io_uring/rsrc.c for the for-next branches, but it'll apply
directly as that with a slight offset:

checking file io_uring/rsrc.c
Hunk #1 succeeded at 56 (offset -10448 lines).

I'll do that, thanks.

-- 
Jens Axboe