Re: [RFC] Patch for isolated scheduler domains

[Nick Piggin <nickpiggin@yahoo.com.au>]

Ingo Molnar wrote:
> * Dimitri Sivanich <sivanich@sgi.com> wrote:
> 
> 
>>I'm interested in implementing something I'll call isolated sched
>>domains for single cpus (to minimize the latencies involved when doing
>>things like load balancing on certain select cpus) on IA64.
>>
>>Below I've included an initial patch to illustrate what I'd like to
>>do.  I know there's been mention of 'platform specific work' in the
>>area of sched domains. This patch only addresses IA64, but could be
>>made generic as well.  The code is derived directly from the current
>>default arch_init_sched_domains code.
> 
> 
> it looks good to me - and i'd suggest to put it into sched.c. Every
> architecture benefits from the ability to define isolated CPUs.
> 

Cool. Have you actually tried running it? With Ingo's correction, it
should work fine but I don't think anyone has tested this.

> One minor nit wrt. this line:
> 
> +               cpu_sd->flags &= ~(SD_BALANCE_NEWIDLE | SD_BALANCE_EXEC |
> + SD_BALANCE_CLONE);  /* Probably redundant */
> 
> i'd suggest to set it to 0. You dont want WAKE_AFFINE nor WAKE_BALANCE
> to move your tasks out of the isolated domain.
> 
> 
>>- Assuming boot time configuration is appropriate ('isolcpus=' in my example),
>>  is allowing boot time configuration of only completely isolated cpus
>>  focusing too narrowly on this one concept, or should a boot time
>>  configuration allow for a broader array of configurations, or would other
>>  types of sched domain configurations be addressed separately?
> 
> 
> i'd prefer to go with this simple solution and wait for actual usage
> patterns to materialize. If it becomes popular we can define a syscall
> to configure the domain hierarchy (maybe even the parameters) runtime.
> 

Seconded.