Hi Greg or Thomas,
0e576acbc1d9600cf2d9b4a141a2554639959d50
nohz: Fix another inconsistency between CONFIG_NO_HZ=n and nohz=off
This fixed an inconsistency about nohz.
Without this patch, When we boot with nohz=off and CONFIG_NO_HZ=Y,
and the system is idle, powertop shows the cpu is always in polling
state. It can affect the performance in some cases.
*without patch*
PowerTOP version 1.13 (C) 2007 Intel Corporation
Cn Avg residency P-states (frequencies)
C0 (cpu running) ( 0.0%) Turbo Mode 0.0%
polling 70.3ms (100.3%) 2.40 Ghz 0.0%
C1 mwait 0.0ms ( 0.0%) 2.27 Ghz 0.0%
C2 mwait 0.0ms ( 0.0%) 2.14 Ghz 0.0%
C3 mwait 0.0ms ( 0.0%) 1.60 Ghz 100.0%
*with patch*
PowerTOP version 1.13 (C) 2007 Intel Corporation
Cn Avg residency P-states (frequencies)
C0 (cpu running) ( 0.3%) Turbo Mode 0.0%
polling 0.0ms ( 0.0%) 2.40 Ghz 0.0%
C1 mwait 0.0ms ( 0.0%) 2.27 Ghz 0.0%
C2 mwait 0.0ms ( 0.0%) 2.14 Ghz 0.0%
C3 mwait 3.9ms (99.7%) 1.60 Ghz 100.0%
This patch looks applicable to stable-3.4 and stable 3.10. It can be
applyed to 3.10 cleanly, but should be added some adjustment for 3.4.
And what do you think?
Thanks,
Rui
-----------------------
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit 0e576acbc1d9600cf2d9b4a141a2554639959d50 upstream
If CONFIG_NO_HZ=n tick_nohz_get_sleep_length() returns NSEC_PER_SEC/HZ.
If CONFIG_NO_HZ=y and the nohz functionality is disabled via the
command line option "nohz=off" or not enabled due to missing hardware
support, then tick_nohz_get_sleep_length() returns 0. That happens
because ts->sleep_length is never set in that case.
Set it to NSEC_PER_SEC/HZ when the NOHZ mode is inactive.
Reported-by: Michal Hocko <mhocko@xxxxxxx>
Reported-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
[xr: Backported to 3.4:
- applied the change to tick_nohz_stop_sched_tick() instead of
can_stop_idle_tick]
Signed-off-by: Rui Xiang <rui.xiang@xxxxxxxxxx>
---
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 638dadf..67106f8 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -296,8 +296,10 @@ static void tick_nohz_stop_sched_tick(struct tick_sched *ts)
tick_do_timer_cpu = TICK_DO_TIMER_NONE;
}
- if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
+ if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
+ ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
return;
+ }
if (need_resched())
return;
--
--
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