[GIT PULL] nohz fixes

[GIT PULL] nohz fixes

[Frederic Weisbecker]

Ingo,

Please pull the timers/urgent branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	timers/urgent

Just one thing you need to know: you reported me that the warning was
"too much" to tell the user that he can't use full dynticks due to unstable tsc.

I discussed that with Steve and we concluded that we could keep the warning but
only trigger it if the user explicitly wants to use the full dynticks which we
deduce by checking if he filled the nohz_full= boot parameter or he selected
CONFIG_NO_HZ_FULL_ALL. This way we make sure that the user knows what's going
on but only if he really expected to use it.

If you still consider the tainting warning to be too much a hammer, even if only
real users are warned, then tell me and I'll change that to some way you
prefer.


Thanks,
	Frederic
---

Li Zhong (1):
      nohz: fix compile warning in tick_nohz_init()

Steven Rostedt (1):
      nohz: Do not warn about unstable tsc unless user uses nohz_full


 kernel/time/tick-sched.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

[PATCH 1/2] nohz: Do not warn about unstable tsc unless user uses nohz_full

[Frederic Weisbecker]

From: Steven Rostedt <rostedt@goodmis.org>

If the user enables CONFIG_NO_HZ_FULL and runs the kernel on a machine
with an unstable TSC, it will produce a WARN_ON dump as well as taint
the kernel. This is a bit extreme for a kernel that just enables a
feature but doesn't use it.

The warning should only happen if the user tries to use the feature by
either adding nohz_full to the kernel command line, or by enabling
CONFIG_NO_HZ_FULL_ALL that makes nohz used on all CPUs at boot up. Note,
this second feature should not (yet) be used by distros or anyone that
doesn't care if NO_HZ is used or not.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/time/tick-sched.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index e80183f..1102534 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -182,7 +182,8 @@ static bool can_stop_full_tick(void)
 		 * Don't allow the user to think they can get
 		 * full NO_HZ with this machine.
 		 */
-		WARN_ONCE(1, "NO_HZ FULL will not work with unstable sched clock");
+		WARN_ONCE(have_nohz_full_mask,
+			  "NO_HZ FULL will not work with unstable sched clock");
 		return false;
 	}
 #endif
-- 
1.7.5.4

[PATCH 2/2] nohz: fix compile warning in tick_nohz_init()

[Frederic Weisbecker]

From: Li Zhong <zhong@linux.vnet.ibm.com>

cpu is not used after commit 5b8621a68fdcd2baf1d3b413726f913a5254d46a

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/time/tick-sched.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1102534..9563c74 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -344,8 +344,6 @@ static int tick_nohz_init_all(void)
 
 void __init tick_nohz_init(void)
 {
-	int cpu;
-
 	if (!have_nohz_full_mask) {
 		if (tick_nohz_init_all() < 0)
 			return;
-- 
1.7.5.4

Re: [GIT PULL] nohz fixes

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> Ingo,
> 
> Please pull the timers/urgent branch that can be found at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	timers/urgent
> 
> Just one thing you need to know: you reported me that the warning was
> "too much" to tell the user that he can't use full dynticks due to unstable tsc.
> 
> I discussed that with Steve and we concluded that we could keep the warning but
> only trigger it if the user explicitly wants to use the full dynticks which we
> deduce by checking if he filled the nohz_full= boot parameter or he selected
> CONFIG_NO_HZ_FULL_ALL. This way we make sure that the user knows what's going
> on but only if he really expected to use it.
> 
> If you still consider the tainting warning to be too much a hammer, even if only
> real users are warned, then tell me and I'll change that to some way you
> prefer.
> 
> 
> Thanks,
> 	Frederic
> ---
> 
> Li Zhong (1):
>       nohz: fix compile warning in tick_nohz_init()
> 
> Steven Rostedt (1):
>       nohz: Do not warn about unstable tsc unless user uses nohz_full
> 
> 
>  kernel/time/tick-sched.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)

Pulled, thanks Frederic!

	Ingo