Re: [PATCH v2 2/2] nohz: make nohz_full imply isolcpus

From: Chris Metcalf
Date: Wed Apr 08 2015 - 10:05:15 EST

On 04/08/2015 05:41 AM, Peter Zijlstra wrote:
On Mon, Apr 06, 2015 at 02:16:45PM -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.
So the Changelog and the patch don't seem to agree with one another.

The Changelog states that nohz_full should depend on isolcpus.

The git commit message says "make nohz_full imply isolcpus".
That's consistent with the code.

The patch implies nohz_full for isolcpus.

These are not the same; and I don't see the argument for the former make
sense for the latter.

In specific isolcpus without nohz_full does make sense.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Acked-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx> ["thumbs up!"]
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at