[PATCH] tick/broadcast: Remove redundant code in tick_check_new_device()

[PATCH] tick/broadcast: Remove redundant code in tick_check_new_device()

[Zhenzhong Duan]

There is no way a timer used as broadcast clockevent device is also used as
percpu tick clockevent device currently.

It's better to put related code in tick_install_broadcast_device(), but I feel
it's harmless to give it back to the clockevents layer. Pls correct me if I'm
wrong.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 kernel/time/tick-common.c |    7 +------
 1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 49edc1c..9bcc866 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -320,13 +320,8 @@ void tick_check_new_device(struct clock_event_device *newdev)
 
 	/*
 	 * Replace the eventually existing device by the new
-	 * device. If the current device is the broadcast device, do
-	 * not give it back to the clockevents layer !
+	 * device.
 	 */
-	if (tick_is_broadcast_device(curdev)) {
-		clockevents_shutdown(curdev);
-		curdev = NULL;
-	}
 	clockevents_exchange_device(curdev, newdev);
 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
-- 
1.7.3

Re: [PATCH] tick/broadcast: Remove redundant code in tick_check_new_device()

[Thomas Gleixner]

On Wed, 8 Nov 2017, Zhenzhong Duan wrote:

> There is no way a timer used as broadcast clockevent device is also used as
> percpu tick clockevent device currently.

Correct.

> It's better to put related code in tick_install_broadcast_device(), but I feel
> it's harmless to give it back to the clockevents layer. Pls correct me if I'm
> wrong.

You already established, that it _cannot_ be the broadcast device and the
per cpu device at the same time. So that condition can never be true. What
do you want to put into tick_install_broadcast_device()? This second
paragraph doesn't make sense, unless I'm missing something.

Thanks,

	tglx

Re: [PATCH] tick/broadcast: Remove redundant code in tick_check_new_device()

[Zhenzhong Duan]

On 2017/11/14 0:54, Thomas Gleixner wrote:

> On Wed, 8 Nov 2017, Zhenzhong Duan wrote:
>
>> There is no way a timer used as broadcast clockevent device is also used as
>> percpu tick clockevent device currently.
> Correct.
>
>> It's better to put related code in tick_install_broadcast_device(), but I feel
>> it's harmless to give it back to the clockevents layer. Pls correct me if I'm
>> wrong.
> You already established, that it _cannot_ be the broadcast device and the
> per cpu device at the same time. So that condition can never be true. What
> do you want to put into tick_install_broadcast_device()? This second
> paragraph doesn't make sense, unless I'm missing something.

I didn't find the reason in long history logs while the comments saying 'If the current device is the broadcast device, do not give it back to the clockevents layer !'

If it does, tick_install_broadcast_device() is a proper place. If not, I can resend the patch with fresh description, pls confirm.

-- 
thanks
zduan

Re: [PATCH] tick/broadcast: Remove redundant code in tick_check_new_device()

[Thomas Gleixner]

On Tue, 14 Nov 2017, Zhenzhong Duan wrote:
> On 2017/11/14 0:54, Thomas Gleixner wrote:
> 
> > On Wed, 8 Nov 2017, Zhenzhong Duan wrote:
> > 
> > > There is no way a timer used as broadcast clockevent device is also used
> > > as
> > > percpu tick clockevent device currently.
> > Correct.
> > 
> > > It's better to put related code in tick_install_broadcast_device(), but I
> > > feel
> > > it's harmless to give it back to the clockevents layer. Pls correct me if
> > > I'm
> > > wrong.
> > You already established, that it _cannot_ be the broadcast device and the
> > per cpu device at the same time. So that condition can never be true. What
> > do you want to put into tick_install_broadcast_device()? This second
> > paragraph doesn't make sense, unless I'm missing something.
> 
> I didn't find the reason in long history logs while the comments saying 'If
> the current device is the broadcast device, do not give it back to the
> clockevents layer !'

To be honest I can't figure it out myself why this was put there, even if I
wrote it myself. Fact is that this is wrong and cannot happen at all.

Thanks,

	tglx