Re: [PATCH v4 10/13] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu()
From: Frederic Weisbecker <frederic@kernel.org>
Date: 2020-10-01 14:44:59
Also in:
linux-arch, linux-arm-kernel, lkml, netdev
On Wed, Jul 22, 2020 at 02:57:33PM +0000, Alex Belits wrote:
quoted hunk ↗ jump to hunk
From: Yuri Norov <redacted> For nohz_full CPUs the desirable behavior is to receive interrupts generated by tick_nohz_full_kick_cpu(). But for hard isolation it's obviously not desirable because it breaks isolation. This patch adds check for it. Signed-off-by: Yuri Norov <redacted> [abelits@marvell.com: updated, only exclude CPUs running isolated tasks] Signed-off-by: Alex Belits <redacted> --- kernel/time/tick-sched.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 6e4cd8459f05..2f82a6daf8fc 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c@@ -20,6 +20,7 @@ #include <linux/sched/clock.h> #include <linux/sched/stat.h> #include <linux/sched/nohz.h> +#include <linux/isolation.h> #include <linux/module.h> #include <linux/irq_work.h> #include <linux/posix-timers.h>@@ -268,7 +269,8 @@ static void tick_nohz_full_kick(void) */ void tick_nohz_full_kick_cpu(int cpu) { - if (!tick_nohz_full_cpu(cpu)) + smp_rmb();
What is it ordering?
+ if (!tick_nohz_full_cpu(cpu) || task_isolation_on_cpu(cpu)) return;
You can't simply ignore an IPI. There is always a reason for a nohz_full CPU to be kicked. Something triggered a tick dependency. It can be posix cpu timers for example, or anything.
irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); -- 2.26.2