Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG_CPU problems

From: Oleg Nesterov
Date: Tue Feb 20 2007 - 15:06:48 EST

On 02/20, Christoph Lameter wrote:
> On Tue, 20 Feb 2007, Max Krasnyansky wrote:
> > > > Well seems that we have a set of unresolved issues with workqueues and cpu
> > > > hotplug.
> >
> > How about storing 'cpu' explicitly in the work queue instead of relying on the
> > smp_processor_id() and friends ? That way there is no ambiguity when
> > threads/timers get
> > moved around.
> The slab functionality is designed to work on the processor with the
> queue. These tricks will only cause more trouble in the future. The
> cache_reaper needs to be either disabled or run on the right processor. It
> should never run on the wrong processor.

I personally agree. Besides, cache_reaper is not alone. Note the comment
in debug_smp_processor_id() about cpu-bound processes. The slab does correct
thing right now, stops the timer on CPU_DEAD. Other problems imho should be
solved by fixing cpu-hotplug. Gautham and Srivatsa are working on that.


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