On Thu, Jul 26, 2007 at 12:22:31PM -0400, Frank Ch. Eigler wrote:
> Hi -
>
> On Thu, Jul 26, 2007 at 11:02:26AM -0400, Mathieu Desnoyers wrote:
> > [...]
> > > > The problem is also in _stp_print_flush, not *only* in relay code:
> > > > void _stp_print_flush (void)
> > > > ...
> > > > spin_lock(&_stp_print_lock);
> > > > spin_unlock(&_stp_print_lock);
> > > >
> > > > Those will turn into mutexes with -rt.
> > >
> > > Indeed,
>
> (Though actually that bug was fixed some time ago.)
>
>
> > > plus systemtap-generated locking code uses rwlocks,
> > > local_irq_save/restore or preempt_disable, in various places. Could
> > > someone point to a place that spells out what would be more
> > > appropriate way of ensuring atomicity while being compatible with -rt?
> >
> > AFAIK, for your needs either:
> > [...]
> > - Use per-cpu data with preempt disabling/irq disabling
>
> As in local_irq_save / preempt_disable? Yes, already done.
>
> > - Use the original "real" spin locks/rwlocks (raw_*).
> > [...]
>
> It was unclear from the OLS paper whether the spin_lock_irq* family of
> functions also had to be moved to the raw forms.
By making the locks of the raw_* type, spin_lock_irq* functions would
then automatically disable hardware interrupts.
>
> > You just don't want to sleep in the tracing code. [...] Since you
> > will likely disable preemption, make sure your tracing code executes
> > in a deterministic time.
>
> Definitely, that has always been the case.
>
> > Make sure that the sub-buffer switch code respects that too [...]
>
> We will review that part of the related code.
>
> - FChE
--
Regards,
Ankita Garg ([email protected])
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India
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