Messages in this thread |  | | | Date | Tue, 29 Jul 2008 17:44:10 -0700 | | From | Jeremy Fitzhardinge <> | | Subject | Re: [PATCH 2/2] x86: implement multiple queues for smp function call IPIs | |
Andi Kleen wrote:
> On Tue, Jul 29, 2008 at 04:32:57PM -0700, Jeremy Fitzhardinge wrote:
>
>> This adds 8 queues for smp_call_function(), in order to avoid a
>>
>
> Now that we have per CPU IDT and there's no global bottleneck anymore
> I think it would be actually fine to use
> more than 8 vectors. 32 or 64 might be a better default.
>
Well, there's no point in having more vectors than CPUs, and a bit of
doubling up doesn't hurt too much. So I think 8 is a good default for
normal sized machines. But I can see that being able to add more
vectors for large machines might be helpful. I guess it really depends
on what the fan-out is for multicast messages.
I dunno, maybe it makes sense to take numa topology into account, on the
assumption that 1) most cross-cpu function calls will be tlb flushes now
(or at least, sending to mm->cpu_vm_mask), and 2) most tlb flushes will
be between cpus within one node.
>> void native_send_call_func_ipi(cpumask_t mask)
>> {
>> cpumask_t allbutself;
>> + unsigned queue = smp_processor_id() % CONFIG_GENERIC_SMP_QUEUES;
>>
>
> Does this really always run with preemption disabled?
Think so, but I'll check again. One of my TODO list items is to check
whether smp_call_function_mask should disable preemption for itself, or
at least WARN_ON if its called with preemption enabled.
J
|  |