Re: [Patch] SMP call function cleanup

[Jan Glauber <glauber@gmx.de>]

On Thu, 2004-04-22 at 15:58, James Bottomley wrote:
> Because to execute on a single cpu it's less efficient than the single
> cpu variant (even with the sparse mask traversal) and the
> smp_call_functions are usually in the critical path, so saving cycles is
> good...

With my patch you would use on_single_cpu:

static inline void on_single_cpu(void (*func) (void *info), void *info,
                                 int nonatomic, int wait, int cpu)
{
        cpumask_t map;

        preempt_disable();
        cpus_clear(map);
        cpu_set(cpu, map);
        on_cpu(func, info, nonatomic, wait, map);
        preempt_enable();
}

so the overhead to the single cpu variant of smp_call_function is 

	cpus_clear(map);
	cpu_set(cpu, map);

on_cpu():
	cpus_and(map, map, cpu_online_map);
	if (cpus_empty(map))
		goto out;

and the for_each loop in on_cpu

I don't know if that overhead is so much that you want to have two smp
call functions.

Jan

---
Jan Glauber
Linux on zSeries Development
IBM Deutschland Entwicklung GmbH
Phone: +49 7031 161911   Mail: jang@de.ibm.com