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

[Raghavendra K T]

On 08/02/2013 01:40 AM, Peter Zijlstra wrote:
> On Thu, Aug 01, 2013 at 11:46:24PM +0530, Raghavendra K T wrote:
> > 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.
>
> I always use early_printk(), but that requires you set up your serial
> console properly and joe-user won't have done that.

Thanks Peter. Yes. this is more convenient.

/me remembers using early_printk  during pvops patch debugging without
setting up serial console ;)

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