Re: [PATCH 2/6] sched: add function to execute a function synchronously on a physical cpu

From: Juergen Gross
Date: Fri Mar 11 2016 - 08:08:08 EST


On 11/03/16 13:57, Peter Zijlstra wrote:
> On Fri, Mar 11, 2016 at 01:48:12PM +0100, Juergen Gross wrote:
>> On 11/03/16 13:42, Peter Zijlstra wrote:
>>> how about something like:
>>>
>>> struct xen_callback_struct {
>>> struct work_struct work;
>>> struct completion done;
> int (*func)(void*);
>>> void * data;
>>> int ret;
>>> };
>>>
>>> static void xen_callback_f(struct work_struct *work)
>>> {
>>> struct xen_callback_struct *xcs = container_of(work, struct xen_callback_struct, work);
>>>
>>> xcs->ret = xcs->func(xcs->data);
>>>
>>> complete(&xcs->done);
>>> }
>>>
>>> xen_call_on_cpu_sync(int cpu, int (*func)(void *), void *data)
>>> {
>>> struct xen_callback_state xcs = {
>>> .work = __WORK_INITIALIZER(xcs.work, xen_callback_f);
>>> .done = COMPLETION_INITIALIZER_ONSTACK(xcs.done),
> .func = func,
>>> .data = data,
>>> };
>>>
>>> queue_work_on(&work, cpu);
>>> wait_for_completion(&xcs.done);
>>>
>>> return xcs.ret;
>>> }
>>>
>>> No mucking about with the scheduler state, no new exported functions
>>> etc..
>>>
>>
>> Hey, I like it. Can't be limited to Xen as on bare metal the function
>> needs to be called on cpu 0, too. But avoiding the scheduler fiddling
>> is much better! As this seems to be required for Dell hardware only,
>> I could add it to some Dell base driver in case you don't want to add
>> it to core code.
>
> Urgh yeah, saw that in your other mail. It looks like I should go look
> at set_cpus_allowed_ptr() abuse :/
>
> Not sure where this would fit best, maybe somewhere near workqueue.c or
> smp.c.

At a first glance I think smp.c would be the better choice. I'll have a try.

Thanks,

Juergen