linux-kernel - Re: [RFC patch] spin_lock: add cross cache lines checking

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Message-ID: <1330917889.18835.46.camel@debian>
Date:	Mon, 05 Mar 2012 11:24:49 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	tglx@...utronix.com
Cc:	mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, andi.kleen@...el.com
Subject: Re: [RFC patch] spin_lock: add cross cache lines checking

Oops.
Sorry, the patch is not tested well! will update it later. 

On Mon, 2012-03-05 at 11:20 +0800, Alex Shi wrote:
> Modern x86 CPU won't hold whole memory bus when executing 'lock'
> prefixed instructions unless the instruction destination is crossing 2
> cache lines. If so, it is disaster of system performance.
> 
> Actually if the lock is not in the 'packed' structure, gcc places it
> safely under x86 arch. But seems add this checking in
> CONFIG_DEBUG_LOCK_ALLOC is harmless.
> 
> btw, change SPIN_BUG_ON macro a little for style complain.
> 
> Inspired-by: Andi Kleen <andi.kleen@...el.com>
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
> diff --git a/arch/x86/include/asm/cache.h b/arch/x86/include/asm/cache.h
> index 48f99f1..79d146e 100644
> --- a/arch/x86/include/asm/cache.h
> +++ b/arch/x86/include/asm/cache.h
> @@ -7,6 +7,8 @@
>  #define L1_CACHE_SHIFT	(CONFIG_X86_L1_CACHE_SHIFT)
>  #define L1_CACHE_BYTES	(1 << L1_CACHE_SHIFT)
>  
> +#define L1_CACHE_SIZE_MASK	(~(L1_CACHE_BYTES - 1)UL)
> +
>  #define __read_mostly __attribute__((__section__(".data..read_mostly")))
>  
>  #define INTERNODE_CACHE_SHIFT CONFIG_X86_INTERNODE_CACHE_SHIFT
> diff --git a/include/asm-generic/cache.h b/include/asm-generic/cache.h
> index 1bfcfe5..244e528 100644
> --- a/include/asm-generic/cache.h
> +++ b/include/asm-generic/cache.h
> @@ -9,4 +9,6 @@
>  #define L1_CACHE_SHIFT		5
>  #define L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)
>  
> +#define L1_CACHE_SIZE_MASK     (~(L1_CACHE_BYTES - 1)UL)
> +
>  #endif /* __ASM_GENERIC_CACHE_H */
> diff --git a/lib/spinlock_debug.c b/lib/spinlock_debug.c
> index 5f3eacd..554dcda 100644
> --- a/lib/spinlock_debug.c
> +++ b/lib/spinlock_debug.c
> @@ -13,6 +13,12 @@
>  #include <linux/delay.h>
>  #include <linux/module.h>
>  
> +#define SPIN_BUG_ON(cond, lock, msg) {if (unlikely(cond)) spin_bug(lock, msg); }
> +
> +#define is_cross_lines(p)						\
> +	(((unsigned long)(p) & L1_CACHE_SIZE_MASK) !=			\
> +	(((unsigned long)(p) + sizeof(*p) - 1) & L1_CACHE_SIZE_MASK))	\
> +
>  void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
>  			  struct lock_class_key *key)
>  {
> @@ -22,6 +28,8 @@ void __raw_spin_lock_init(raw_spinlock_t *lock, const char *name,
>  	 */
>  	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
>  	lockdep_init_map(&lock->dep_map, name, key, 0);
> +	SPIN_BUG_ON(is_cross_lines(lock->raw_lock), lock,
> +			"!!! the lock cross cache lines !!!");
>  #endif
>  	lock->raw_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
>  	lock->magic = SPINLOCK_MAGIC;
> @@ -40,6 +48,8 @@ void __rwlock_init(rwlock_t *lock, const char *name,
>  	 */
>  	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
>  	lockdep_init_map(&lock->dep_map, name, key, 0);
> +	SPIN_BUG_ON(is_cross_lines(lock->raw_lock), lock,
> +			"!!! the lock cross cache lines !!!");
>  #endif
>  	lock->raw_lock = (arch_rwlock_t) __ARCH_RW_LOCK_UNLOCKED;
>  	lock->magic = RWLOCK_MAGIC;
> @@ -75,8 +85,6 @@ static void spin_bug(raw_spinlock_t *lock, const char *msg)
>  	spin_dump(lock, msg);
>  }
>  
> -#define SPIN_BUG_ON(cond, lock, msg) if (unlikely(cond)) spin_bug(lock, msg)
> -
>  static inline void
>  debug_spin_lock_before(raw_spinlock_t *lock)
>  {
> 


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