From: Peter Zijlstra <peterz@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
keescook@chromium.org,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] block: switch to atomic_t for request references
Date: Tue, 7 Dec 2021 21:28:31 +0100 [thread overview]
Message-ID: <20211207202831.GA18361@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <Ya9hdlBuWYUWRQzs@hirez.programming.kicks-ass.net>
On Tue, Dec 07, 2021 at 02:28:22PM +0100, Peter Zijlstra wrote:
> For refcount_inc(), as extracted from alloc_perf_context(), I get:
>
> 4b68: b8 01 00 00 00 mov $0x1,%eax
> 4b6d: f0 0f c1 43 28 lock xadd %eax,0x28(%rbx)
> 4b72: 85 c0 test %eax,%eax
> 4b74: 74 1b je 4b91 <alloc_perf_context+0xf1>
> 4b76: 8d 50 01 lea 0x1(%rax),%edx
> 4b79: 09 c2 or %eax,%edx
> 4b7b: 78 20 js 4b9d <alloc_perf_context+0xfd>
>
> the best I can seem to find is: https://godbolt.org/z/ne5o6eEEW
Argh.. __atomic_add_fetch() != __atomic_fetch_add(); much confusion for
GCC having both. With the right primitive it becomes:
movl $1, %eax
lock xaddl %eax, (%rdi)
testl %eax, %eax
je .L5
js .L6
Which makes a whole lot more sense.
next prev parent reply other threads:[~2021-12-07 20:28 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-03 15:35 [PATCH] block: switch to atomic_t for request references Jens Axboe
2021-12-03 15:56 ` Keith Busch
2021-12-06 6:53 ` Christoph Hellwig
2021-12-06 8:31 ` Peter Zijlstra
2021-12-06 16:32 ` Jens Axboe
2021-12-06 17:19 ` Peter Zijlstra
2021-12-06 17:35 ` Linus Torvalds
2021-12-06 18:13 ` Jens Axboe
2021-12-06 20:51 ` Kees Cook
2021-12-06 21:17 ` Linus Torvalds
2021-12-06 23:28 ` Kees Cook
2021-12-07 0:13 ` Linus Torvalds
2021-12-07 4:56 ` Kees Cook
2021-12-07 9:34 ` Peter Zijlstra
2021-12-07 16:03 ` Linus Torvalds
2021-12-07 10:30 ` Peter Zijlstra
2021-12-07 16:10 ` Linus Torvalds
2021-12-07 16:23 ` Peter Zijlstra
2021-12-06 16:31 ` Jens Axboe
2021-12-07 11:26 ` Peter Zijlstra
2021-12-07 13:28 ` Peter Zijlstra
2021-12-07 15:51 ` Peter Zijlstra
2021-12-07 16:13 ` Linus Torvalds
2021-12-07 16:52 ` Peter Zijlstra
2021-12-07 17:41 ` Peter Zijlstra
2021-12-07 17:43 ` Linus Torvalds
2021-12-07 17:45 ` Linus Torvalds
2021-12-07 20:28 ` Peter Zijlstra [this message]
2021-12-07 23:23 ` Linus Torvalds
2021-12-08 17:07 ` Peter Zijlstra
2021-12-08 18:00 ` Linus Torvalds
2021-12-08 18:44 ` Peter Zijlstra
2021-12-08 18:50 ` Linus Torvalds
2021-12-08 20:32 ` Peter Zijlstra
2021-12-10 10:57 ` Peter Zijlstra
2021-12-10 12:38 ` Peter Zijlstra
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