Messages in this thread | | | Date | Mon, 14 Sep 2015 15:02:52 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt |
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On 09/14/2015 09:57 AM, Peter Zijlstra wrote: > On Fri, Sep 11, 2015 at 02:37:37PM -0400, Waiman Long wrote: >> +#define queued_spin_trylock(l) pv_queued_spin_trylock_unfair(l) >> +static inline bool pv_queued_spin_trylock_unfair(struct qspinlock *lock) >> +{ >> + struct __qspinlock *l = (void *)lock; >> + >> + if (READ_ONCE(l->locked)) >> + return 0; >> + /* >> + * Wait a bit here to ensure that an actively spinning vCPU has a fair >> + * chance of getting the lock. >> + */ >> + cpu_relax(); >> + >> + return cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0; >> +} >> +static inline int pvstat_trylock_unfair(struct qspinlock *lock) >> +{ >> + int ret = pv_queued_spin_trylock_unfair(lock); >> + >> + if (ret) >> + pvstat_inc(pvstat_utrylock); >> + return ret; >> +} >> +#undef queued_spin_trylock >> +#define queued_spin_trylock(l) pvstat_trylock_unfair(l) > These aren't actually ever used...
The pvstat_trylock_unfair() is within the CONFIG_QUEUED_LOCK_STAT block. It will only be activated when the config parameter is set. Otherwise, pv_queued_spin_trylock_unfair() will be used without any counting.
It is used provide count of how many unfair trylock has successfully got the lock.
Cheers, Longman
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