lkml.org 
[lkml]   [2007]   [Jul]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Question] Hooks for scheduler tracing (CFS)
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.

> 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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-07-26 18:27    [W:0.065 / U:0.148 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site