Weird schedule delay time for cache_reap()

Weird schedule delay time for cache_reap()

[Chen, Kenneth W]

I can't convince myself that the 2nd argument in schedule_delayed_work
called from cache_reap() function make any sense:


static void cache_reap(void *unused)
{ ...

        check_irq_on();
        up(&cache_chain_sem);
        drain_remote_pages();
        /* Setup the next iteration */
        schedule_delayed_work(&__get_cpu_var(reap_work), REAPTIMEOUT_CPUC + smp_processor_id());
}


Suppose one have a lucky 1024-processor big iron numa box,
cpu0 will do cache_reap every 2 sec (REAPTIMEOUT_CPUC = 2*HZ).
cpu512 will do cache_reap every 4 sec,
cpu1023 will do cache_reap every 6 sec.

Is the skew intentional on different CPU?  Why different interval for
different cpu#?

- Ken

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: Weird schedule delay time for cache_reap()

[Andi Kleen]

On Thursday 27 October 2005 04:28, Chen, Kenneth W wrote:
> can't convince myself that the 2nd argument in schedule_delayed_work
>called from cache_reap() function make any sense:


>static void cache_reap(void *unused)
>{ ...
>schedule_delayed_work(&__get_cpu_var(reap_work), REAPTIMEOUT_CPUC + 
smp_processor_id());
>
> Suppose one have a lucky 1024-processor big iron numa box,
> cpu0 will do cache_reap every 2 sec (REAPTIMEOUT_CPUC = 2*HZ).
> cpu512 will do cache_reap every 4 sec,
> cpu1023 will do cache_reap every 6 sec.
>
> Is the skew intentional on different CPU?  Why different interval for
> different cpu#?

It looks like a buggy attempt to make the timers not cluster.
The +smp_processor_id() should be probably only done on the first iteration.
start_cpu_timer() does this already, so removing it should be ok.

-Andi

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>