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


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