Re: [PATCH v9 1/5] qrwlock: A queue read/write lock implementation

[Waiman Long]

On 01/20/2014 10:21 AM, Peter Zijlstra wrote:
> On Tue, Jan 14, 2014 at 11:44:03PM -0500, Waiman Long wrote:
> > +#ifndef arch_mutex_cpu_relax
> > +# define arch_mutex_cpu_relax() cpu_relax()
> > +#endif
> Include<linux/mutex.h>

Will do so.

> > +#ifndef smp_load_acquire
> > +# ifdef CONFIG_X86
> > +#   define smp_load_acquire(p)				\
> > +	({						\
> > +		typeof(*p) ___p1 = ACCESS_ONCE(*p);	\
> > +		barrier();				\
> > +		___p1;					\
> > +	})
> > +# else
> > +#   define smp_load_acquire(p)				\
> > +	({						\
> > +		typeof(*p) ___p1 = ACCESS_ONCE(*p);	\
> > +		smp_mb();				\
> > +		___p1;					\
> > +	})
> > +# endif
> > +#endif
> > +
> > +#ifndef smp_store_release
> > +# ifdef CONFIG_X86
> > +#   define smp_store_release(p, v)			\
> > +	do {						\
> > +		barrier();				\
> > +		ACCESS_ONCE(*p) = v;			\
> > +	} while (0)
> > +# else
> > +#   define smp_store_release(p, v)			\
> > +	do {						\
> > +		smp_mb();				\
> > +		ACCESS_ONCE(*p) = v;			\
> > +	} while (0)
> > +# endif
> > +#endif
> Remove these.

Will do that.

> > +/*
> > + * If an xadd (exchange-add) macro isn't available, simulate one with
> > + * the atomic_add_return() function.
> > + */
> > +#ifdef xadd
> > +# define qrw_xadd(rw, inc)	xadd(&(rw).rwc, inc)
> > +#else
> > +# define qrw_xadd(rw, inc)	(u32)(atomic_add_return(inc,&(rw).rwa) - inc)
> > +#endif
> Is GCC really so stupid that you cannot always use the
> atomic_add_return()? The x86 atomic_add_return is i + xadd(), so you'll
> end up with:
>
>   i + xadd() - i
>
> Surely it can just remove the two i terms?

I guess gcc should do the right thing. I will remove the macro.

> > +/**
> > + * wait_in_queue - Add to queue and wait until it is at the head
> > + * @lock: Pointer to queue rwlock structure
> > + * @node: Node pointer to be added to the queue
> > + */
> > +static inline void wait_in_queue(struct qrwlock *lock, struct qrwnode *node)
> > +{
> > +	struct qrwnode *prev;
> > +
> > +	node->next = NULL;
> > +	node->wait = true;
> > +	prev = xchg(&lock->waitq, node);
> > +	if (prev) {
> > +		prev->next = node;
> > +		/*
> > +		 * Wait until the waiting flag is off
> > +		 */
> > +		while (smp_load_acquire(&node->wait))
> > +			arch_mutex_cpu_relax();
> > +	}
> > +}
> Please rebase on top of the MCS lock patches such that this is gone.

I would like to keep this as long as the MCS patches have not been 
merged into tip. However, I will take that out if the MCS patches are in 
when I need to revise the qrwlock patches.

-Longman
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/