On 07/27/2015 03:39 PM, Davidlohr Bueso wrote:
On Mon, 2015-07-27 at 13:30 -0400, Waiman Long wrote:
The pending bit acts as a 1-slot waiting queue. So if the vCPU needs to
fall back to regular queuing, it needs to clear the bit.
Right, that's what I thought. So you would also need to call
clear_pending() as soon as the trylock/pending loop hits zero. Or am I
missing something?
/*
* trylock || pending
*/
for (;;) {
...
if (loop--<= 0) {
clear_pending(lock);
goto queue;
}
}
Also, no need to check for negative loop, zero should be enough to
breakout.
The while loop below can potentially make the loop variable become negative:
/*
* wait for in-progress pending->locked hand-overs
*/
if (val == _Q_PENDING_VAL) {
while (((val = atomic_read(&lock->val)) ==
_Q_PENDING_VAL) &&
loop--)
cpu_relax();
}
Cheers,
Longman
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