On Mon, 19 Dec 2005, Matthew Wilcox wrote: > On Mon, Dec 19, 2005 at 09:27:44AM +0000, Russell King wrote: > > > mov r0, #1 > > > swp r1, r0, [%0] > > > cmp r1, #0 > > > bne __contention > > > That's over-simplified, and is the easy bit. Now work out how you handle > > the unlock operation. > > > > You don't know whether the lock is contended or not in the unlock path, > > so you always have to do the "wake up" thing. (You can't rely on the > > value of the lock since another thread may well be between this swp > > instruction and entering the __contention function. Hence you can't > > use the value of the lock to determine whether there's anyone sleeping > > on it.) > > Here's a slightly less efficient way to determine if anyone else has > swp'd behind your back (apologies if I get my ARM assembly wrong, it's > been a few years):
No need to be less efficient. See the mail I just sent with additional details. Nicolas - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
