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From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
	Jakub Jelinek <jakub@redhat.com>
Subject: Re: [PATCH] x86: Optimize variable_test_bit()
Date: Mon, 4 May 2015 15:42:57 +0200	[thread overview]
Message-ID: <20150504134257.GA16478@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150501151630.GH5029@twins.programming.kicks-ass.net>

On Fri, May 01, 2015 at 05:16:30PM +0200, Peter Zijlstra wrote:

> diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
> index cfe3b954d5e4..bcf4fa77c04f 100644
> --- a/arch/x86/include/asm/bitops.h
> +++ b/arch/x86/include/asm/bitops.h
> @@ -313,6 +313,15 @@ static __always_inline int constant_test_bit(long nr, const volatile unsigned lo
>  
>  static inline int variable_test_bit(long nr, volatile const unsigned long *addr)
>  {
> +#ifdef CC_HAVE_ASM_GOTO
> +	asm_volatile_goto ("bt %1, %0\n\t"
> +			   "jc %l[cc_label]"
> +			   : : "m" (*(unsigned long *)addr), "Ir" (nr)
> +			   : : cc_label);
> +	return 0;
> +cc_label:
> +	return 1;
> +#else

I figured I'd try both jc and jnc versions:

   text           data     bss     dec            hex   filename
12203914        1738112 1081344 15023370         e53d0a defconfig-build/vmlinux
12204228        1738112 1081344 15023684         e53e44 defconfig-build/vmlinux-jc
12203240        1738112 1081344 15022696         e53a68 defconfig-build/vmlinux-jnc

Clearly I picked the wrong one :-) It also shows there is real value in
exposing this decision to GCC.

      parent reply	other threads:[~2015-05-04 13:43 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-01 15:16 [PATCH] x86: Optimize variable_test_bit() Peter Zijlstra
2015-05-01 16:03 ` Linus Torvalds
2015-05-01 16:16   ` Peter Zijlstra
2015-05-01 16:29     ` Peter Zijlstra
2015-05-01 16:18   ` Peter Zijlstra
2015-05-01 16:33   ` Jakub Jelinek
2015-05-01 16:45     ` Linus Torvalds
2015-05-01 16:46     ` Peter Zijlstra
2015-05-01 17:17       ` Ingo Molnar
2015-05-01 19:02     ` Vladimir Makarov
2015-05-01 20:49       ` Linus Torvalds
2015-05-01 22:22         ` Vladimir Makarov
2015-05-02 12:39         ` Peter Zijlstra
2015-05-04 15:37           ` Richard Henderson
2015-05-04 19:33           ` [RFC] Design for flag bit outputs from asms Richard Henderson
2015-05-04 20:14             ` H. Peter Anvin
2015-05-04 20:27               ` H. Peter Anvin
2015-05-04 20:33               ` Richard Henderson
2015-05-04 20:45                 ` Linus Torvalds
2015-05-04 20:57                   ` Richard Henderson
2015-05-04 21:23                     ` H. Peter Anvin
2015-05-04 20:35               ` Linus Torvalds
2015-05-04 20:42                 ` H. Peter Anvin
2015-05-05  9:01             ` Gabriel Paubert
2015-05-05 13:50             ` Segher Boessenkool
2015-05-05 15:37               ` Linus Torvalds
2015-05-05 16:10                 ` Segher Boessenkool
2015-05-02 12:43       ` [PATCH] x86: Optimize variable_test_bit() Peter Zijlstra
2015-05-04 18:07         ` Vladimir Makarov
2015-05-04 20:14           ` H. Peter Anvin
2015-05-04 13:42 ` Peter Zijlstra [this message]

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