linux-kernel - Re: [PATCH RFC 0/7] x86: convert ticketlocks to C and remove duplicate code

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Message-ID: <4E0240AC.9060603@goop.org>
Date:	Wed, 22 Jun 2011 12:21:16 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH RFC 0/7] x86: convert ticketlocks to C and remove duplicate
 code

On 06/21/2011 07:01 AM, Peter Zijlstra wrote:
> One other thing you could contemplate is adding something like:
>
> #define xadd(ptr, inc)							\
> do {									\
> 	switch(sizeof(*(ptr))) {					\
> 	case 1:								\
> 		asm volatile (LOCK_PREFIX "xaddb %0, %1\n"		\
>                              : "+r" (inc), "+m" (*(ptr))		\
>                              : : "memory", "cc");			\
> 	case 2:
> 		... xaddw ...
> 	case 4:
> 		... xaddl ...
> } while (0)
>
> and a similar something for inc. For both there seem to be various asm
> bits left (we could even consider adding xadd to
> arch/x86/include/asm/cmpxchg*.h).

A friend just pointed out that gcc has a "__sync_fetch_and_add()"
intrinsic, which compiles to xadd when used in this context.  What's the
general feeling about using these kinds of gcc features?

It also has __sync_bool_compare_and_swap(), which would simplify a lot
of asm/cmpxchg.h...

    J
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