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SubjectRe: SLAB cache reaper on isolated cpus
Christoph Lameter wrote:
> On Tue, 20 Feb 2007, Max Krasnyansky wrote:
>> Suppose I need to isolate a CPU. We already support at the scheduler and
>> irq levels (irq affinity). But I want to go a bit further and avoid
>> doing kernel work on isolated cpus as much as possible. For example I
>> would not want to schedule work queues and stuff on them. Currently
>> there are just a few users of the schedule_delayed_work_on(). cpufreq
>> (don't care for isolation purposes), oprofile (same here) and slab. For
>> the slab it'd be nice to run the reaper on some other CPU. But you're
>> saying that locking depends on CPU pinning. Is there any other option
>> besides disabling cache reap ? Is there a way for example to constraint
>> the slabs on CPU X to not exceed N megs ?
> There is no way to constrain the amount of slab work. In order to make the
> above work we would have to disable the per cpu caches for a certain cpu.
> Then there would be no need to run the cache reaper at all.
> To some extend such functionality already exists. F.e. kmalloc_node()
> already bypasses the per cpu caches (most of the time). kmalloc_node will
> have to take a spinlock on a shared cacheline on each invocation. kmalloc
> does only touch per cpu data during regular operations. Thus kmalloc() is much
> faster than kmalloc_node() and the cachelines for kmalloc() can be kept in
> the per cpu cache.
> If we could disable all per cpu caches for certain cpus then you could
> make this work. All slab OS interference would be off the processor.

Hmm. That's an idea. I'll play with it later today or tomorrow.


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