linux-kernel - [PATCH] idle/tick-broadcast: Exit cpu idle poll loop when cleared from tick_broadcast_force

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150119052754.20256.54721.stgit@preeti.in.ibm.com>
Date:	Mon, 19 Jan 2015 10:57:54 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	tglx@...utronix.de
Cc:	peterz@...radead.org, linuxppc-dev@...ts.ozlabs.org,
	mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] idle/tick-broadcast: Exit cpu idle poll loop when cleared
 from tick_broadcast_force_mask

An idle cpu enters cpu_idle_poll() if it is set in the tick_broadcast_force_mask.
This is so that it does not incur the overhead of entering idle states when it is expected
to be woken up anytime then through a broadcast IPI. The condition that forces an exit out
of the idle polling is the check on setting of the TIF_NEED_RESCHED flag for the idle thread.

When the broadcast IPI does arrive, it is not guarenteed that the handler sets the
TIF_NEED_RESCHED flag. Hence although the cpu is cleared in the tick_broadcast_force_mask,
it continues to loop in cpu_idle_poll unnecessarily wasting power. Hence exit the idle
poll loop if the tick_broadcast_force_mask gets cleared and enter idle states.

Of course if the cpu has entered cpu_idle_poll() on being asked to poll explicitly,
it continues to poll till it is asked to reschedule.

Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
---

 kernel/sched/idle.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index c47fce7..aaf1c1d 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void)
 	rcu_idle_enter();
 	trace_cpu_idle_rcuidle(0, smp_processor_id());
 	local_irq_enable();
-	while (!tif_need_resched())
+	while (!tif_need_resched() &&
+		(cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 	rcu_idle_exit();

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/