spin_is_locked() broken for uniprocessor?

Leon Woestenberg leon.woestenberg at gmail.com
Wed Aug 19 21:16:48 EST 2009


On Wed, Aug 19, 2009 at 12:53 PM, Alan Cox<alan at lxorguk.ukuu.org.uk> wrote:
> On Wed, 19 Aug 2009 10:38:06 +0100
> in drivers because there is driver code that uses spin_is_locked() in
> fairly sensible fashion when dealing with locking.
One use is to measure lock contention hits on a particular spin lock.

However I wonder if there are tracing capabilities to measure lock
contention on a particular lock?

Currently I have inserted code much like this to get a feeling on the

this_cpu = get_cpu();
contention = spin_is_locked(&lock);
if (contention) {
  /* spin lock was contended, prev_cpu, this_cpu */
  /* no hard guarantee, as we had a possible race inbetween
is_locked() and lock(), but works for driver/irq spin lock */

/* critical section */

prev_cpu = this_cpu;


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