Re: [PATCH 2/2] nohz: make nohz_full imply isolcpus

From: Chris Metcalf
Date: Fri Apr 03 2015 - 15:20:46 EST

On 04/03/2015 01:42 PM, Frederic Weisbecker wrote:
On Fri, Apr 03, 2015 at 12:24:08PM -0400, cmetcalf@xxxxxxxxxx wrote:
From: Chris Metcalf <cmetcalf@xxxxxxxxxx>

It's not clear that nohz_full is useful without isolcpus also
set, since otherwise the scheduler has to run periodically to
try to determine whether to steal work from other cores.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
I think Rick has a similar patch.

I didn't see anything relevant in linux-next, though I did see cpu_isolated_map
made into a public symbol in a recent commit by Rik.

Rik, what's the change you're proposing that's similar to this one? Thanks!

I am puzzled why this has not been done before, so I suspect
there is some argument against it that I am missing, but I
wasn't able to turn anything up by searching LKML.

kernel/sched/core.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f0f831e8a345..275f12c608f2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6836,6 +6836,7 @@ static int init_sched_domains(const struct cpumask *cpu_map)
doms_cur = alloc_sched_domains(ndoms_cur);
if (!doms_cur)
doms_cur = &fallback_doms;
+ tick_nohz_full_set_cpus(cpu_isolated_map);
cpumask_andnot(doms_cur[0], cpu_map, cpu_isolated_map);
err = build_sched_domains(doms_cur[0], NULL);

Chris Metcalf, EZChip Semiconductor

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