[PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Robert Joslyn]

This branch is needed to allow preemptible IRQs to be scheduled,
otherwise the kernel hangs during boot on my e300 based platforms.
This branch is needed for both CONFIG_PREEMPT and CONFIG_PREEMPT_RT,
so broaden the check to CONFIG_PREEMPTION, which is selected by both.

This was previously set to CONFIG_PREEMPTION, but was reverted as part
of removing LAZY_PREEMPT support.

Fixes: b33022a48c79
Signed-off-by: Robert Joslyn <robert_joslyn@selinc.com>
---
 arch/powerpc/kernel/interrupt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index af62ec974b97..970039af8e92 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 		/* Returning to a kernel context with local irqs enabled. */
 		WARN_ON_ONCE(!(regs->msr & MSR_EE));
 again:
-		if (IS_ENABLED(CONFIG_PREEMPT)) {
+		if (IS_ENABLED(CONFIG_PREEMPTION)) {
 			/* Return to preemptible kernel context */
 			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
 				if (preempt_count() == 0)
-- 
2.45.2

Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
> This branch is needed to allow preemptible IRQs to be scheduled,
> otherwise the kernel hangs during boot on my e300 based platforms.
> This branch is needed for both CONFIG_PREEMPT and CONFIG_PREEMPT_RT,
> so broaden the check to CONFIG_PREEMPTION, which is selected by both.
> 
> This was previously set to CONFIG_PREEMPTION, but was reverted as part
> of removing LAZY_PREEMPT support.

I remember I pointed this out while Shrikanth posted the preempt-lazy
patches but didn't realize that I need this in RT tree, too.

The lazy-preempt patches for powerpc were merged upstream, I am going to
pull them into the v6.6-series.
I am going to Cc you, hopefully you can confirm that it is working.

> Fixes: b33022a48c79
> Signed-off-by: Robert Joslyn <robert_joslyn@selinc.com>
> ---
>  arch/powerpc/kernel/interrupt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index af62ec974b97..970039af8e92 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
>  		/* Returning to a kernel context with local irqs enabled. */
>  		WARN_ON_ONCE(!(regs->msr & MSR_EE));
>  again:
> -		if (IS_ENABLED(CONFIG_PREEMPT)) {
> +		if (IS_ENABLED(CONFIG_PREEMPTION)) {
>  			/* Return to preemptible kernel context */
>  			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
>  				if (preempt_count() == 0)

Sebastian

Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2025-01-07 12:56:08 [+0100], To Robert Joslyn wrote:
> On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
> > This branch is needed to allow preemptible IRQs to be scheduled,
> > otherwise the kernel hangs during boot on my e300 based platforms.
> > This branch is needed for both CONFIG_PREEMPT and CONFIG_PREEMPT_RT,
> > so broaden the check to CONFIG_PREEMPTION, which is selected by both.
> > 
> > This was previously set to CONFIG_PREEMPTION, but was reverted as part
> > of removing LAZY_PREEMPT support.
> 
> I remember I pointed this out while Shrikanth posted the preempt-lazy
> patches but didn't realize that I need this in RT tree, too.
> 
> The lazy-preempt patches for powerpc were merged upstream, I am going to
> pull them into the v6.6-series.
> I am going to Cc you, hopefully you can confirm that it is working.

Robert, you are referring to v6.6-RT, correct?

Sebastian

RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Robert Joslyn]

> -----Original Message-----
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Sent: Tuesday, January 7, 2025 3:59 AM
> To: Robert Joslyn <robert_joslyn@selinc.com>
> Cc: linux-kernel@vger.kernel.org; linux-rt-users@vger.kernel.org;
> tglx@linutronix.de; rostedt@goodmis.org; Shrikanth Hegde
> <sshegde@linux.ibm.com>
> Subject: Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT
> 
> [Caution - External]
> 
> On 2025-01-07 12:56:08 [+0100], To Robert Joslyn wrote:
> > On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
> > > This branch is needed to allow preemptible IRQs to be scheduled,
> > > otherwise the kernel hangs during boot on my e300 based platforms.
> > > This branch is needed for both CONFIG_PREEMPT and
> CONFIG_PREEMPT_RT,
> > > so broaden the check to CONFIG_PREEMPTION, which is selected by both.
> > >
> > > This was previously set to CONFIG_PREEMPTION, but was reverted as
> > > part of removing LAZY_PREEMPT support.
> >
> > I remember I pointed this out while Shrikanth posted the preempt-lazy
> > patches but didn't realize that I need this in RT tree, too.
> >
> > The lazy-preempt patches for powerpc were merged upstream, I am going
> > to pull them into the v6.6-series.
> > I am going to Cc you, hopefully you can confirm that it is working.
> 
> Robert, you are referring to v6.6-RT, correct?
> 
> Sebastian

Yes, I'm using 6.6.58-rt45 at the moment. We found this regression while trying to update from 5.10-rt. I haven't played with lazy-preempt yet but I can certainly test the patches, presently we run everything with PREEMPT_RT.

Thanks,
Robert

Re: RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2025-01-07 18:09:46 [+0000], Robert Joslyn wrote:
> 
> Yes, I'm using 6.6.58-rt45 at the moment. We found this regression
> while trying to update from 5.10-rt. I haven't played with
> lazy-preempt yet but I can certainly test the patches, presently we
> run everything with PREEMPT_RT.

So I released v6.12.8-rt8 and v6.13-rc6-rt3. Looking at the lazy bits I
think I just forward your patch to the stable queue for v6.6.

> Thanks,
> Robert

Sebastian

RE: RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Robert Joslyn]

> -----Original Message-----
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Sent: Thursday, January 9, 2025 3:44 AM
> To: Robert Joslyn <robert_joslyn@selinc.com>
> Cc: linux-kernel@vger.kernel.org; linux-rt-users@vger.kernel.org;
> tglx@linutronix.de; rostedt@goodmis.org; Shrikanth Hegde
> <sshegde@linux.ibm.com>
> Subject: Re: RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT
> 
> [Caution - External]
> 
> On 2025-01-07 18:09:46 [+0000], Robert Joslyn wrote:
> >
> > Yes, I'm using 6.6.58-rt45 at the moment. We found this regression
> > while trying to update from 5.10-rt. I haven't played with
> > lazy-preempt yet but I can certainly test the patches, presently we
> > run everything with PREEMPT_RT.
> 
> So I released v6.12.8-rt8 and v6.13-rc6-rt3. Looking at the lazy bits I think I
> just forward your patch to the stable queue for v6.6.

I did some basic testing on 6.12.8-rt8 and that worked fine with both preempt_lazy and preempt_rt.

For what it's worth, we've been using the patch for 6.6-rt for about a month now in internal testing and haven't seen any other issues.

Thanks!
Robert

Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Shrikanth Hegde]

On 1/7/25 17:26, Sebastian Andrzej Siewior wrote:
> On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
>> This branch is needed to allow preemptible IRQs to be scheduled,
>> otherwise the kernel hangs during boot on my e300 based platforms.
>> This branch is needed for both CONFIG_PREEMPT and CONFIG_PREEMPT_RT,

Hi Robert.

Are you running with preempt=full or enabled preempt_rt ?
rt is yet to be supported on powerpc. are you having it enabled out of tree?

Also, I have sent out patch to enable dynamic preemption. It uses preempt_model_preemptible.
I think it should work for you as well. If you could give that a try and ensure it works, it would be great.
https://lore.kernel.org/all/20250106051919.55020-2-sshegde@linux.ibm.com/

>> so broaden the check to CONFIG_PREEMPTION, which is selected by both.
>>
>> This was previously set to CONFIG_PREEMPTION, but was reverted as part
>> of removing LAZY_PREEMPT support.
> 
> I remember I pointed this out while Shrikanth posted the preempt-lazy
> patches but didn't realize that I need this in RT tree, too.
> 
> The lazy-preempt patches for powerpc were merged upstream, I am going to
> pull them into the v6.6-series.
> I am going to Cc you, hopefully you can confirm that it is working.
> 
>> Fixes: b33022a48c79
>> Signed-off-by: Robert Joslyn <robert_joslyn@selinc.com>
>> ---
>>   arch/powerpc/kernel/interrupt.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
>> index af62ec974b97..970039af8e92 100644
>> --- a/arch/powerpc/kernel/interrupt.c
>> +++ b/arch/powerpc/kernel/interrupt.c
>> @@ -396,7 +396,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
>>   		/* Returning to a kernel context with local irqs enabled. */
>>   		WARN_ON_ONCE(!(regs->msr & MSR_EE));
>>   again:
>> -		if (IS_ENABLED(CONFIG_PREEMPT)) {
>> +		if (IS_ENABLED(CONFIG_PREEMPTION)) {
>>   			/* Return to preemptible kernel context */
>>   			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
>>   				if (preempt_count() == 0)
> 
> Sebastian

RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Robert Joslyn]

> -----Original Message-----
> From: Shrikanth Hegde <sshegde@linux.ibm.com>
> Sent: Tuesday, January 7, 2025 5:10 AM
> To: Robert Joslyn <robert_joslyn@selinc.com>
> Cc: linux-kernel@vger.kernel.org; linux-rt-users@vger.kernel.org;
> tglx@linutronix.de; rostedt@goodmis.org; Sebastian Andrzej Siewior
> <bigeasy@linutronix.de>
> Subject: Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT
> 
> [Caution - External]
> 
> On 1/7/25 17:26, Sebastian Andrzej Siewior wrote:
> > On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
> >> This branch is needed to allow preemptible IRQs to be scheduled,
> >> otherwise the kernel hangs during boot on my e300 based platforms.
> >> This branch is needed for both CONFIG_PREEMPT and
> CONFIG_PREEMPT_RT,
> 
> Hi Robert.
> 
> Are you running with preempt=full or enabled preempt_rt ?
> rt is yet to be supported on powerpc. are you having it enabled out of tree?

I'm running PREEMPT_RT using the out of tree patches on 6.6.58-rt45:
https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git/

I haven't tried using the mainline kernel, since as you said, it doesn't have powerpc support for PREEMPT_RT yet.

> 
> Also, I have sent out patch to enable dynamic preemption. It uses
> preempt_model_preemptible.
> I think it should work for you as well. If you could give that a try and ensure it
> works, it would be great.
> https://urldefense.com/v3/__https://lore.kernel.org/all/20250106051919.5
> 5020-2-
> sshegde@linux.ibm.com/__;!!O7uE89YCNVw!IDeomstGeuiEZi9FmLHH8C2xo
> PPo_ewL-
> k2kiQ9CmVID35U4J_v3Dkafjo3RnS9ygPoUZWwyyp91SP2euRkKArk$

Does the dynamic preemption support let me enable the same functionality as PREEMPT_RT with the out of tree patches? I can test it out either way.

Thanks,
Robert

Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

[Shrikanth Hegde]

On 1/7/25 23:43, Robert Joslyn wrote:
>> -----Original Message-----
>> From: Shrikanth Hegde <sshegde@linux.ibm.com>
>> Sent: Tuesday, January 7, 2025 5:10 AM
>> To: Robert Joslyn <robert_joslyn@selinc.com>
>> Cc: linux-kernel@vger.kernel.org; linux-rt-users@vger.kernel.org;
>> tglx@linutronix.de; rostedt@goodmis.org; Sebastian Andrzej Siewior
>> <bigeasy@linutronix.de>
>> Subject: Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT
>>
>> [Caution - External]
>>
>> On 1/7/25 17:26, Sebastian Andrzej Siewior wrote:
>>> On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
>>>> This branch is needed to allow preemptible IRQs to be scheduled,
>>>> otherwise the kernel hangs during boot on my e300 based platforms.
>>>> This branch is needed for both CONFIG_PREEMPT and
>> CONFIG_PREEMPT_RT,
>>
>> Hi Robert.
>>
>> Are you running with preempt=full or enabled preempt_rt ?
>> rt is yet to be supported on powerpc. are you having it enabled out of tree?
> 
> I'm running PREEMPT_RT using the out of tree patches on 6.6.58-rt45:
> https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git/
> 
> I haven't tried using the mainline kernel, since as you said, it doesn't have powerpc support for PREEMPT_RT yet.
> 
>>
>> Also, I have sent out patch to enable dynamic preemption. It uses
>> preempt_model_preemptible.
>> I think it should work for you as well. If you could give that a try and ensure it
>> works, it would be great.
>> https://urldefense.com/v3/__https://lore.kernel.org/all/20250106051919.5
>> 5020-2-
>> sshegde@linux.ibm.com/__;!!O7uE89YCNVw!IDeomstGeuiEZi9FmLHH8C2xo
>> PPo_ewL-
>> k2kiQ9CmVID35U4J_v3Dkafjo3RnS9ygPoUZWwyyp91SP2euRkKArk$
> 
> Does the dynamic preemption support let me enable the same functionality as PREEMPT_RT with the out of tree patches? I can test it out either way.
> 


with preempt_rt, dynamic preemption allows you to switch between full 
and lazy. without preempt_rt, you can switch between none, 
voluntary,full and lazy.


> Thanks,
> Robert