* Peter Zijlstra <[email protected]> wrote:
> On Tue, Oct 08, 2013 at 09:21:14AM +0200, Ingo Molnar wrote:
> >
> > * Christoph Lameter <[email protected]> wrote:
> >
> > > SNMP stats are not protected by preemption but by bh handling.
> >
> > Most forms of bh exclusion work via the preemption count though, and
> > softirq contexts themselves are generally not preemptible [to other CPUs]
> > either.
> >
> > So the warnings should, in most cases, not trigger.
>
> Right, so softirqs run either in the irq tail at which point
> preempt_count += SOFTIRQ_OFFSET and thus preemption is disabled, or it
> runs in ksoftirqd which has strict cpu affinity which also disables the
> warning, and it also increments preempt_count with SOFTIRQ_OFFSET to
> exclude the softirq from interrupts while its running, also disabling
> the warning.
A third context would be syscall-level code that runs with
local_bh_disable()/enable() - but that too ought to have the preempt count
elevated.
> So it should very much not trigger.. if it does you want to know about
> it.
Yes. If nothing else then for the education value.
Thanks,
Ingo
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