Re: [PATCH RFC 1/2] qspinlock: Introducing a 4-byte queue spinlockimplementation

From: Raghavendra K T
Date: Thu Aug 01 2013 - 14:10:26 EST

On 08/01/2013 11:28 PM, Waiman Long wrote:
On 08/01/2013 05:40 AM, Peter Zijlstra wrote:
On Wed, Jul 31, 2013 at 10:37:10PM -0400, Waiman Long wrote:


+ */
+ for (qn_idx = 1; qn_idx< MAX_QNODES; qn_idx++) {
+ if (!node[qn_idx].used)
+ break;

+ if (unlikely(qn_idx == MAX_QNODES)) {
+ /*
+ * This shouldn't happen, print a warning message
+ *& busy spinning on the lock.
+ */
+ pr_warn("qspinlock: queue node table exhausted at "
+ "cpu %d!\n", cpu_nr);
This could make your machine die hard.. not all contexts can printk().

Do you have any suggestion? I could skip the warning and silently do the
busy spinning. I just want some way to notify the user of this rare event.

We have used debugfs in pv-spinlock to avoid that since printk uses
spinlock again. may be it will help to profile many other parts of
code too.

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