On Mon, 2005-12-19 at 00:00 -0500, Steven Rostedt wrote:
> On Mon, 2005-12-19 at 02:37 +0100, Ingo Molnar wrote:
> > +static inline int
> > +__mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter,
> > + struct thread_info *ti, struct task_struct *task,
> > + unsigned long *flags, unsigned long task_state
> > __IP_DECL__)
> > +{
> > + unsigned int old_val;
> > +
> > + debug_lock_irqsave(&debug_lock, *flags, ti);
> > + DEBUG_WARN_ON(lock->magic != lock);
> > +
>
> How expensive is the xchg? Since __mutex_lock_common is called even
> when it's going to wake up. Maybe it might be more efficient to add
> something like:
But add:
#ifdef MUTEX_LOCKLESS_FASTPATH
>
> if (atomic_cmpxchg(&lock->count, 1, 0) {
> debug_set_owner(lock, ti __IP__);
> debug_unlock_irqrestore(&debug_lock, *flags, ti);
> return 1;
> }
#endif
-- Steve
>
> This way we save the overhead of grabbing another spinlock, adding the
> task to the wait_list and changing it's state.
>
>
> > + spin_lock(&lock->wait_lock);
> > + __add_waiter(lock, waiter, ti, task __IP__);
> > + set_task_state(task, task_state);
> > +
> > + /*
> > + * Lets try to take the lock again - this is needed even if
> > + * we get here for the first time (shortly after failing to
> > + * acquire the lock), to make sure that we get a wakeup once
> > + * it's unlocked. Later on this is the operation that gives
> > + * us the lock. We need to xchg it to -1, so that when we
> > + * release the lock, we properly wake up other waiters!
> > + */
> > + old_val = atomic_xchg(&lock->count, -1);
> > +
> > + if (old_val == 1) {
>
> -- Steve
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
--
Steven Rostedt
Senior Programmer
Kihon Technologies
(607)786-4830
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
