From: David Daney <ddaney@caviumnetworks.com>
To: Coly Li <bosong.ly@taobao.com>
Cc: Wang Cong <xiyou.wangcong@gmail.com>,
Jeremy Fitzhardinge <jeremy@goop.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
Yong Zhang <yong.zhang0@gmail.com>
Subject: Re: [PATCH 2/7] PowerPC: add unlikely() to BUG_ON()
Date: Thu, 27 Jan 2011 09:57:39 -0800 [thread overview]
Message-ID: <4D41B213.4070606@caviumnetworks.com> (raw)
In-Reply-To: <1296130356-29896-3-git-send-email-bosong.ly@taobao.com>
Why not also CC the PPC maintainers as well? I am not certain, but I
think they may be reached at:
linuxppc-dev@lists.ozlabs.org
On 01/27/2011 04:12 AM, Coly Li wrote:
> Current BUG_ON() arch/powerpc/include/asm/bug.h does not use unlikely(),
> in order to get better branch predict result, source code may have to call
> BUG_ON() with unlikely() explicitly. This is not a suggested method
> to use BUG_ON().
>
> This patch adds unlikely() inside BUG_ON implementation on PPC
> code, callers can use BUG_ON without explicit unlikely() now.
>
> I don't have any PPC hardware to compile and test this fix, any feedback
> of this patch is welcome.
>
> Signed-off-by: Coly Li<bosong.ly@taobao.com>
> Cc: Jeremy Fitzhardinge<jeremy@goop.org>
> Cc: David Daney<ddaney@caviumnetworks.com>
> Cc: Wang Cong<xiyou.wangcong@gmail.com>
> Cc: Yong Zhang<yong.zhang0@gmail.com>
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 065c590..10889a6 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -2,6 +2,7 @@
> #define _ASM_POWERPC_BUG_H
> #ifdef __KERNEL__
>
> +#include<linux/compiler.h>
> #include<asm/asm-compat.h>
>
> /*
> @@ -71,7 +72,7 @@
> unreachable(); \
> } while (0)
>
> -#define BUG_ON(x) do { \
> +#define __BUG_ON(x) do { \
> if (__builtin_constant_p(x)) { \
> if (x) \
> BUG(); \
> @@ -85,6 +86,8 @@
> } \
> } while (0)
>
> +#define BUG_ON(x) __BUG_ON(unlikely(x))
> +
This is the same type of frobbing you were trying to do to MIPS.
I will let the powerpc maintainers weigh in on it, but my opinion is
that, as with MIPS, BUG_ON() is expanded to a single machine
instruction, and this unlikely() business will not change the generated
code in any useful way. It is thus gratuitous code churn and
complexification.
David Daney
> #define __WARN_TAINT(taint) do { \
> __asm__ __volatile__( \
> "1: twi 31,0,0\n" \
WARNING: multiple messages have this Message-ID (diff)
From: David Daney <ddaney@caviumnetworks.com>
To: Coly Li <bosong.ly@taobao.com>
Cc: linux-kernel@vger.kernel.org,
Jeremy Fitzhardinge <jeremy@goop.org>,
Wang Cong <xiyou.wangcong@gmail.com>,
Yong Zhang <yong.zhang0@gmail.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2/7] PowerPC: add unlikely() to BUG_ON()
Date: Thu, 27 Jan 2011 09:57:39 -0800 [thread overview]
Message-ID: <4D41B213.4070606@caviumnetworks.com> (raw)
In-Reply-To: <1296130356-29896-3-git-send-email-bosong.ly@taobao.com>
Why not also CC the PPC maintainers as well? I am not certain, but I
think they may be reached at:
linuxppc-dev@lists.ozlabs.org
On 01/27/2011 04:12 AM, Coly Li wrote:
> Current BUG_ON() arch/powerpc/include/asm/bug.h does not use unlikely(),
> in order to get better branch predict result, source code may have to call
> BUG_ON() with unlikely() explicitly. This is not a suggested method
> to use BUG_ON().
>
> This patch adds unlikely() inside BUG_ON implementation on PPC
> code, callers can use BUG_ON without explicit unlikely() now.
>
> I don't have any PPC hardware to compile and test this fix, any feedback
> of this patch is welcome.
>
> Signed-off-by: Coly Li<bosong.ly@taobao.com>
> Cc: Jeremy Fitzhardinge<jeremy@goop.org>
> Cc: David Daney<ddaney@caviumnetworks.com>
> Cc: Wang Cong<xiyou.wangcong@gmail.com>
> Cc: Yong Zhang<yong.zhang0@gmail.com>
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 065c590..10889a6 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -2,6 +2,7 @@
> #define _ASM_POWERPC_BUG_H
> #ifdef __KERNEL__
>
> +#include<linux/compiler.h>
> #include<asm/asm-compat.h>
>
> /*
> @@ -71,7 +72,7 @@
> unreachable(); \
> } while (0)
>
> -#define BUG_ON(x) do { \
> +#define __BUG_ON(x) do { \
> if (__builtin_constant_p(x)) { \
> if (x) \
> BUG(); \
> @@ -85,6 +86,8 @@
> } \
> } while (0)
>
> +#define BUG_ON(x) __BUG_ON(unlikely(x))
> +
This is the same type of frobbing you were trying to do to MIPS.
I will let the powerpc maintainers weigh in on it, but my opinion is
that, as with MIPS, BUG_ON() is expanded to a single machine
instruction, and this unlikely() business will not change the generated
code in any useful way. It is thus gratuitous code churn and
complexification.
David Daney
> #define __WARN_TAINT(taint) do { \
> __asm__ __volatile__( \
> "1: twi 31,0,0\n" \
next prev parent reply other threads:[~2011-01-27 17:57 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-27 12:12 [PATCH 0/6] use BUG_ON correctly, v2 Coly Li
2011-01-27 12:12 ` [PATCH 1/7] MIPS: add unlikely() to BUG_ON() Coly Li
2011-01-27 17:50 ` David Daney
2011-01-28 10:41 ` Coly Li
2011-01-27 12:12 ` [PATCH 2/7] PowerPC: " Coly Li
2011-01-27 17:57 ` David Daney [this message]
2011-01-27 17:57 ` David Daney
2011-01-27 20:04 ` Scott Wood
2011-01-27 20:04 ` Scott Wood
2011-01-27 20:32 ` David Daney
2011-01-27 20:32 ` David Daney
2011-01-28 9:05 ` David Laight
2011-01-28 9:05 ` David Laight
[not found] ` <AE90C24D6B3A694183C094C60CF0A2F6D8AC2D__37237.0892241181$1296205746$gmane$org@saturn3.aculab.com>
2011-01-28 10:14 ` Andreas Schwab
2011-01-28 10:14 ` Andreas Schwab
2011-01-28 11:02 ` Coly Li
2011-01-28 11:02 ` Coly Li
2011-01-27 12:12 ` [PATCH 3/7] dma: use BUG_ON correctly in iop-adma.c Coly Li
2011-01-27 12:12 ` [PATCH 4/7] dma: use BUG_ON correctly in mv_xor.c Coly Li
2011-01-27 12:12 ` [PATCH 5/7] dma: use BUG_ON correctly in ppc4xx/adam.c Coly Li
2011-01-27 12:12 ` [PATCH 6/7] wl_cfg80211.c: use BUG_ON correctly Coly Li
2011-01-27 12:12 ` [PATCH 7/7] scsi_lib.c: " Coly Li
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