[PATCH] ARM: tegra: cpuidle: use CPUIDLE_FLAG_TIMER_STOP flag
Joseph Lo
josephl at nvidia.com
Thu Jul 18 07:08:45 EDT 2013
On Thu, 2013-07-18 at 04:31 +0800, Stephen Warren wrote:
> On 07/17/2013 04:15 AM, Joseph Lo wrote:
> > On Wed, 2013-07-17 at 03:51 +0800, Stephen Warren wrote:
> >> On 07/16/2013 05:17 AM, Joseph Lo wrote:
> >>> On Tue, 2013-07-16 at 02:04 +0800, Stephen Warren wrote:
> >>>> On 06/25/2013 03:23 AM, Joseph Lo wrote:
> >>>>> Use the CPUIDLE_FLAG_TIMER_STOP and let the cpuidle framework
> >>>>> to handle the CLOCK_EVT_NOTIFY_BROADCAST_ENTER/EXIT when entering
> >>>>> this state.
> ... [ discussion of issues with Joesph's patches applied]
> >
> > OK. I did more stress tests last night and today. I found it cause by
> > the patch "ARM: tegra: cpuidle: use CPUIDLE_FLAG_TIMER_STOP flag" and
> > only impact the Tegra20 platform. The hot plug regression seems due to
> > this patch. After dropping this patch on top of v3.11-rc1, the Tegra20
> > can back to normal.
> >
> > And the hop plug and suspend stress test can pass on Tegra30/114 too.
> >
> > Can the other two patch series for Tegra114 to support CPU idle power
> > down mode and system suspend still moving forward, not be blocked by
> > this patch?
> >
> > Looks the CPUIDLE_FLAG_TIMER_STOP flag still cause some other issue for
> > hot plug on Tegra20, I will continue to check this. You can just drop
> > this patch.
>
> OK, if I drop that patch, then everything on Tegra20 and Tegra30 seems
> fine again.
>
> However, I've found some new and exciting issue on Tegra114!
>
> With unmodified v3.11-rc1, I can do the following without issue:
>
> * Unplug/replug CPUs, so that I had all combinations of CPU 1, 2, 3
> plugged/unpplugged (with CPU 0 always plugged).
>
> * Unplug/replug CPUs, so that I had all combinations of CPU 0, 1, 2, 3
> plugged/unpplugged (with the obvious exception of never having all CPUs
> unplugged).
>
> However, if I try this with your Tegra114 cpuidle and suspend patches
> applied, I see the following issues:
>
> 1) If I boot, unplug CPU 0, then replug CPU 0, the system immediately
> hard-hangs.
>
Sorry, I didn't apply the hotplug stress test on CPU0 too much. Because
all of our use cases and stress tests are focused on secondary CPUs
only.
After doing some tests, here is my summary. This issue happens after we
support CPU idle power-down mode and relates to PMC or flow controller I
believe.
i) on top of v3.11-rc1 (only support WFI in CPU idle)
When hot unplug CPU0, the PMC can power gate and put it into reset
state. This is what I expect and also true on all the other secondary
CPUs. The flow controller can maintain the CPU power state machine as
what we want.
ii) on top of v3.11-rc1 + CPU idle power down mode support
a) I saw most of the time the CPU0,1,2,3 were in power down and reset
status. That means the idle power down mode works fine.
b) Testing with the CPU hotplug stress test with the secondary CPUs (not
include CPU0), the result is good too.
c) Testing hot plug on CPU0 with CPUIDLE_FLAG_TIMER_STOP apply or not
apply (Note 1), the result shows not good to me. The CPU0 have already
gone into WFI and the flow controller is set as WAITFOREVENT mode. But
the PMC always can't power gate CPU0 and sometimes can put it into
reset, but sometimes can't. That's why you can see it hanging after
unplug CPU0 sometimes.
When hop plug-in CPU0, because the CPU0 not be power gated by PMC or the
flow controller event that we trigger PMC to do. I think it may need
more time to process it. It can be solved by just add a udelay(10) after
we set up flow controller event to wake up CPU0. Then it can put CPU0
back to normal state.
So the result shows to me the flow controller (or the state machine)
looks not support to power gate CPU0 when we support idle power down
mode. The power of CPU0 also can bind to the power of the CPU cluster.
That cause the state machine can't work correctly in this case, I guess.
I need to check with some people. BTW, I just saw we drop the hotplug
support for CPU0 in downstream rel-18 (although it's not related to this
issue).
Note 1.
diff --git a/arch/arm/mach-tegra/cpuidle-tegra114.c
b/arch/arm/mach-tegra/cpuidle-tegra114.c
index 658b205..5248a69 100644
--- a/arch/arm/mach-tegra/cpuidle-tegra114.c
+++ b/arch/arm/mach-tegra/cpuidle-tegra114.c
@@ -43,8 +43,12 @@ static int tegra114_idle_power_down(struct
cpuidle_device *dev,
tegra_set_cpu_in_lp2();
cpu_pm_enter();
+ clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
+
cpu_suspend(0, tegra30_sleep_cpu_secondary_finish);
+ clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
+
cpu_pm_exit();
tegra_clear_cpu_in_lp2();
@@ -66,8 +70,8 @@ static struct cpuidle_driver tegra_idle_driver = {
.exit_latency = 500,
.target_residency = 1000,
.power_usage = 0,
- .flags =
CPUIDLE_FLAG_TIME_VALID |
-
CPUIDLE_FLAG_TIMER_STOP,
+ .flags =
CPUIDLE_FLAG_TIME_VALID,
+//
CPUIDLE_FLAG_TIMER_STOP,
.name = "powered-down",
.desc = "CPU power gated",
},
> 2) If I run the hotplug test script, leaving CPU 0 always present, I
> sometimes see:
>
> > root at localhost:~# for i in `seq 1 50`; do echo ITERATION $i; ./cpuonline.py; done
> > ITERATION 1
> > echo 0 > /sys/devices/system/cpu/cpu2/online
> > [ 458.910054] CPU2: shutdown
> > echo 0 > /sys/devices/system/cpu/cpu1/online
> > [ 461.004371] CPU1: shutdown
> > echo 0 > /sys/devices/system/cpu/cpu3/online
> > [ 463.027341] CPU3: shutdown
> > echo 1 > /sys/devices/system/cpu/cpu1/online
> > [ 465.061412] CPU1: Booted secondary processor
> > echo 1 > /sys/devices/system/cpu/cpu2/online
> > [ 467.095313] CPU2: Booted secondary processor
> > [ 467.113243] ------------[ cut here ]------------
> > [ 467.117948] WARNING: CPU: 2 PID: 0 at kernel/time/tick-broadcast.c:667 tick_broadcast_oneshot_control+0x19c/0x1c4()
> > [ 467.128352] Modules linked in:
> > [ 467.131455] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 3.11.0-rc1-00022-g7487363-dirty #49
> > [ 467.139678] [<c0015620>] (unwind_backtrace+0x0/0xf8) from [<c001154c>] (show_stack+0x10/0x14)
> > [ 467.148228] [<c001154c>] (show_stack+0x10/0x14) from [<c05135a8>] (dump_stack+0x80/0xc4)
> > [ 467.156336] [<c05135a8>] (dump_stack+0x80/0xc4) from [<c0024590>] (warn_slowpath_common+0x64/0x88)
> > [ 467.165300] [<c0024590>] (warn_slowpath_common+0x64/0x88) from [<c00245d0>] (warn_slowpath_null+0x1c/0x24)
> > [ 467.174959] [<c00245d0>] (warn_slowpath_null+0x1c/0x24) from [<c00695e4>] (tick_broadcast_oneshot_control+0x19c/0x1c4)
> > [ 467.185659] [<c00695e4>] (tick_broadcast_oneshot_control+0x19c/0x1c4) from [<c0067cdc>] (clockevents_notify+0x1b0/0x1dc)
> > [ 467.196538] [<c0067cdc>] (clockevents_notify+0x1b0/0x1dc) from [<c034f348>] (cpuidle_idle_call+0x11c/0x168)
> > [ 467.206292] [<c034f348>] (cpuidle_idle_call+0x11c/0x168) from [<c000f134>] (arch_cpu_idle+0x8/0x38)
> > [ 467.215359] [<c000f134>] (arch_cpu_idle+0x8/0x38) from [<c0061038>] (cpu_startup_entry+0x60/0x134)
> > [ 467.224325] [<c0061038>] (cpu_startup_entry+0x60/0x134) from [<800083d8>] (0x800083d8)
> > [ 467.232227] ---[ end trace ea579be22a00e7fb ]---
> > echo 0 > /sys/devices/system/cpu/cpu1/online
> > [ 469.126682] CPU1: shutdown
Hmm. It's hard to reproduce. But finally, I also can repro with CPU
hotplug stress test. And some strange issues after apply
CPUIDLE_FLAG_TIMER_STOP on Tegra20, can we postpone to apply this?
I need more time to investigate how does this flag impact system.
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