From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthias Kaehlcke <mka@chromium.org>,
Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
James Y Knight <jyknight@google.com>,
Chandler Carruth <chandlerc@google.com>,
Stephen Hines <srhines@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@google.com>,
Guenter Roeck <groeck@chromium.org>,
Greg Hackmann <ghackmann@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [GIT PULL] x86/build changes for v4.17
Date: Thu, 5 Apr 2018 09:24:01 +0200 [thread overview]
Message-ID: <20180405072401.GO4043@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CA+55aFyHzKg3GzTdW4Z+xC5u2FZ8HnduNFi3PYVTGoKCqpR6Dg@mail.gmail.com>
On Wed, Apr 04, 2018 at 05:05:25PM -0700, Linus Torvalds wrote:
> for some reason the test_bit() case looks like
> this:
>
> #define test_bit(nr, addr) \
> (__builtin_constant_p((nr)) \
> ? constant_test_bit((nr), (addr)) \
> : variable_test_bit((nr), (addr)))
>
> which is much more straightforward anyway. I'm not quite sure why we
> did it that odd way anyway, but I bet it's just "hysterical raisins"
> along with the test_bit() not needing inline asm at all for the
> constant case.
I always assumed BT was a more expensive instruction than AND with
immediate.
next prev parent reply other threads:[~2018-04-05 7:24 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-02 9:50 Ingo Molnar
2018-04-02 21:44 ` Linus Torvalds
2018-04-02 22:38 ` Matthias Kaehlcke
2018-04-03 1:26 ` Matthias Kaehlcke
2018-04-03 8:59 ` Peter Zijlstra
2018-04-03 9:51 ` Ingo Molnar
2018-04-03 12:09 ` Peter Zijlstra
2018-04-03 18:06 ` Matthias Kaehlcke
2018-04-03 21:58 ` Nick Desaulniers
2018-04-04 9:19 ` Peter Zijlstra
2018-04-04 9:38 ` Greg KH
2018-04-04 16:49 ` Nick Desaulniers
2018-04-04 17:13 ` Linus Torvalds
2018-04-04 17:46 ` Nick Desaulniers
2018-04-04 23:10 ` Nick Desaulniers
2018-04-04 16:53 ` Nick Desaulniers
2018-04-04 16:59 ` Greg KH
2018-04-04 19:26 ` James Y Knight
2018-04-04 19:42 ` Linus Torvalds
2018-04-04 22:21 ` James Y Knight
2018-04-04 22:29 ` Linus Torvalds
2018-04-05 7:08 ` Peter Zijlstra
2018-04-05 16:21 ` James Y Knight
2018-04-04 19:32 ` Josh Poimboeuf
2018-06-07 19:23 ` Nick Desaulniers
2018-06-07 20:11 ` Greg KH
2018-04-04 9:30 ` Peter Zijlstra
2018-04-04 19:17 ` Matthias Kaehlcke
2018-04-04 20:33 ` Arnd Bergmann
2018-04-04 20:58 ` Matthias Kaehlcke
2018-04-04 21:11 ` Arnd Bergmann
2018-04-04 21:46 ` Matthias Kaehlcke
2018-04-04 21:59 ` Linus Torvalds
2018-04-04 22:17 ` Matthias Kaehlcke
2018-04-04 22:39 ` Linus Torvalds
2018-04-04 23:31 ` Matthias Kaehlcke
2018-04-05 0:05 ` Linus Torvalds
2018-04-05 0:20 ` Kees Cook
2018-04-05 7:24 ` Peter Zijlstra [this message]
2018-04-05 8:04 ` Ingo Molnar
2018-04-05 8:24 ` Peter Zijlstra
2018-04-05 16:43 ` Linus Torvalds
2018-04-05 7:20 ` Peter Zijlstra
2018-04-05 17:46 ` James Y Knight
2018-04-05 18:06 ` Linus Torvalds
2018-04-05 20:51 ` James Y Knight
2018-04-05 21:13 ` Linus Torvalds
2018-04-05 22:51 ` James Y Knight
2018-04-06 2:02 ` Linus Torvalds
2018-04-05 17:47 ` James Y Knight
2018-04-04 23:04 ` Nick Desaulniers
2018-04-03 17:36 ` Linus Torvalds
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