linux-kernel - Re: [PATCH, RFC] sched: update_top_cache_domain only at the times of building sched domain.

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Date:	Tue, 23 Jul 2013 18:53:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC] sched: update_top_cache_domain only at the times of
 building sched domain.

On Tue, Jul 23, 2013 at 10:20:20PM +0600, Rakib Mullick wrote:

> You mean using sd == NULL rather than using update_cache_domain variable ?

Yes, note how:

@@ -6109,7 +6110,7 @@ static void detach_destroy_domains(const struct cpumask *cpu_map)

        rcu_read_lock();
        for_each_cpu(i, cpu_map)
-               cpu_attach_domain(NULL, &def_root_domain, i);
        rcu_read_unlock();
 }

Always has NULL for sd? Which means you can do:

@@ -5138,7 +5138,8 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
        rcu_assign_pointer(rq->sd, sd);
        destroy_sched_domains(tmp, cpu);

-       update_top_cache_domain(cpu);
+       if (sd)
+               update_top_cache_domain(cpu);
 }

 /* cpus with isolated domains */
--
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