linux-kernel - Re: [PATCH RFC ticketlock] Auto-queued ticketlock

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Date:	Mon, 10 Jun 2013 16:47:58 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, sbw@....edu,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH RFC ticketlock] Auto-queued ticketlock

On Sun, 2013-06-09 at 12:36 -0700, Paul E. McKenney wrote:

> --- a/arch/x86/include/asm/spinlock_types.h
> +++ b/arch/x86/include/asm/spinlock_types.h
> @@ -7,12 +7,18 @@
>  
>  #include <linux/types.h>
>  
> -#if (CONFIG_NR_CPUS < 256)
> +#if (CONFIG_NR_CPUS < 128)
>  typedef u8  __ticket_t;
>  typedef u16 __ticketpair_t;
> -#else
> +#define TICKET_T_CMP_GE(a, b) (UCHAR_MAX / 2 >= (unsigned char)((a) - (b)))
> +#elif (CONFIG_NR_CPUS < 32768)
>  typedef u16 __ticket_t;
>  typedef u32 __ticketpair_t;
> +#define TICKET_T_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
> +#else
> +typedef u32 __ticket_t;
> +typedef u64 __ticketpair_t;
> +#define TICKET_T_CMP_GE(a, b) (UINT_MAX / 2 >= (unsigned int)((a) - (b)))
>  #endif
>  
>  #define TICKET_SHIFT	(sizeof(__ticket_t) * 8)
> @@ -21,7 +27,11 @@ typedef struct arch_spinlock {
>  	union {
>  		__ticketpair_t head_tail;
>  		struct __raw_tickets {
> +#ifdef __BIG_ENDIAN__

Is there such a thing as a BIG_ENDIAN x86 box? This is in
arch/x86/include/asm/spinlock_types.h

-- Steve

> +			__ticket_t tail, head;
> +#else /* #ifdef __BIG_ENDIAN__ */
>  			__ticket_t head, tail;
> +#endif /* #else #ifdef __BIG_ENDIAN__ */
>  		} tickets;
>  	};
>  } arch_spinlock_t;


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