[PATCH] powerpc: Add preempt lazy support

[PATCH] powerpc: Add preempt lazy support

[Shrikanth Hegde]

Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
16 bit range of NEED_RESCHED, so compiler can issue single andi. 

Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for 
return to kernel. 

Ran a few benchmarks and db workload on Power10. Performance is close to
preempt=none/voluntary. It is possible that some patterns would
differ in lazy[2]. More details of preempt lazy is here [1]

Since Powerpc system can have large core count and large memory, 
preempt lazy is going to be helpful in avoiding soft lockup issues. 

[1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
[2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 arch/powerpc/Kconfig                   | 1 +
 arch/powerpc/include/asm/thread_info.h | 9 ++++++---
 arch/powerpc/kernel/interrupt.c        | 4 ++--
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 8094a01974cc..2f625aecf94b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -145,6 +145,7 @@ config PPC
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PHYS_TO_DMA
 	select ARCH_HAS_PMEM_API
+	select ARCH_HAS_PREEMPT_LAZY
 	select ARCH_HAS_PTE_DEVMAP		if PPC_BOOK3S_64
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SCALED_CPUTIME		if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 6ebca2996f18..2785c7462ebf 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -103,6 +103,7 @@ void arch_setup_new_exec(void);
 #define TIF_PATCH_PENDING	6	/* pending live patching update */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SINGLESTEP		8	/* singlestepping active */
+#define TIF_NEED_RESCHED_LAZY	9       /* Scheduler driven lazy preemption */
 #define TIF_SECCOMP		10	/* secure computing */
 #define TIF_RESTOREALL		11	/* Restore all regs (implies NOERROR) */
 #define TIF_NOERROR		12	/* Force successful syscall return */
@@ -122,6 +123,7 @@ void arch_setup_new_exec(void);
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
+#define _TIF_NEED_RESCHED_LAZY	(1<<TIF_NEED_RESCHED_LAZY)
 #define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1<<TIF_32BIT)
@@ -142,9 +144,10 @@ void arch_setup_new_exec(void);
 				 _TIF_SYSCALL_EMU)
 
 #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
-				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
-				 _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \
-				 _TIF_NOTIFY_SIGNAL)
+				 _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_RESUME | \
+				 _TIF_UPROBE | _TIF_RESTORE_TM | \
+				 _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL)
+
 #define _TIF_PERSYSCALL_MASK	(_TIF_RESTOREALL|_TIF_NOERROR)
 
 /* Bits in local_flags */
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index af62ec974b97..8f4acc55407b 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -185,7 +185,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
 	ti_flags = read_thread_flags();
 	while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
 		local_irq_enable();
-		if (ti_flags & _TIF_NEED_RESCHED) {
+		if (ti_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
 			schedule();
 		} else {
 			/*
@@ -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)
-- 
2.43.5

Re: [PATCH] powerpc: Add preempt lazy support

[Sebastian Andrzej Siewior]

On 2024-11-08 15:48:53 [+0530], Shrikanth Hegde wrote:
> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
> 16 bit range of NEED_RESCHED, so compiler can issue single andi. 
> 
> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for 
> return to kernel. 
> 
> Ran a few benchmarks and db workload on Power10. Performance is close to
> preempt=none/voluntary. It is possible that some patterns would
> differ in lazy[2]. More details of preempt lazy is here [1]
> 
> Since Powerpc system can have large core count and large memory, 
> preempt lazy is going to be helpful in avoiding soft lockup issues. 
> 
> [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/

The lazy bits are only in tip.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index af62ec974b97..8f4acc55407b 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)

Shouldn't exit_vmx_usercopy() get also this
s@CONFIG_PREEMPT@CONFIG_PREEMPTION@ change ?

Sebastian

Re: [PATCH] powerpc: Add preempt lazy support

[Ankur Arora]

Shrikanth Hegde <sshegde@linux.ibm.com> writes:

> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>
> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
> return to kernel.
>
> Ran a few benchmarks and db workload on Power10. Performance is close to
> preempt=none/voluntary. It is possible that some patterns would
> differ in lazy[2]. More details of preempt lazy is here [1]
>
> Since Powerpc system can have large core count and large memory,
> preempt lazy is going to be helpful in avoiding soft lockup issues.
>
> [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/
>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>

Looks good. Reviewed-by: <ankur.a.arora@oracle.com>

However, I just checked and powerpc does not have
CONFIG_KVM_XFER_TO_GUEST_WORK. Do you need this additional patch
for handling the lazy bit at KVM guest entry?

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index f14329989e9a..7bdf7015bb65 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -84,7 +84,8 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
        hard_irq_disable();

        while (true) {
-               if (need_resched()) {
+               unsigned long tf = read_thread_flags();
+               if (tf & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
                        local_irq_enable();
                        cond_resched();
                        hard_irq_disable();


Ankur

Re: [PATCH] powerpc: Add preempt lazy support

[Shrikanth Hegde]

Thank you Sebastian for taking a look and rwb tag.

> On 2024-11-08 15:48:53 [+0530], Shrikanth Hegde wrote:
>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>
>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>> return to kernel.
>>
>> Ran a few benchmarks and db workload on Power10. Performance is close to
>> preempt=none/voluntary. It is possible that some patterns would
>> differ in lazy[2]. More details of preempt lazy is here [1]
>>
>> Since Powerpc system can have large core count and large memory,
>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>
>> [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
>> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/
> 
> The lazy bits are only in tip.
>

Hi Michael, I sent it to powerpc tree since all the changes were in 
arch/powerpc. Please let me know if i have send it to tip tree instead.


> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>> ---
>> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
>> index af62ec974b97..8f4acc55407b 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)
> 
> Shouldn't exit_vmx_usercopy() get also this
> s@CONFIG_PREEMPT@CONFIG_PREEMPTION@ change ?
> 

I had seen this, but wasn't sure. Will take a look at it.
Thanks for the pointers.

> Sebastian

Re: [PATCH] powerpc: Add preempt lazy support

[Shrikanth Hegde]

On 11/9/24 00:36, Ankur Arora wrote:
> 
> Shrikanth Hegde <sshegde@linux.ibm.com> writes:
> 
>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>
>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>> return to kernel.
>>
>> Ran a few benchmarks and db workload on Power10. Performance is close to
>> preempt=none/voluntary. It is possible that some patterns would
>> differ in lazy[2]. More details of preempt lazy is here [1]
>>
>> Since Powerpc system can have large core count and large memory,
>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>
>> [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
>> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/
>>
>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> 
> Looks good. Reviewed-by: <ankur.a.arora@oracle.com>

Thank you Ankur for taking a look and rwb tag.

> 
> However, I just checked and powerpc does not have
> CONFIG_KVM_XFER_TO_GUEST_WORK. Do you need this additional patch
> for handling the lazy bit at KVM guest entry?

will take a look. Thanks for the pointers.

> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index f14329989e9a..7bdf7015bb65 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -84,7 +84,8 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>          hard_irq_disable();
> 
>          while (true) {
> -               if (need_resched()) {
> +               unsigned long tf = read_thread_flags();
> +               if (tf & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
>                          local_irq_enable();
>                          cond_resched();
>                          hard_irq_disable();
> 
> 
> Ankur

Re: [PATCH] powerpc: Add preempt lazy support

[Michael Ellerman]

Shrikanth Hegde <sshegde@linux.ibm.com> writes:
> Thank you Sebastian for taking a look and rwb tag.
>
>> On 2024-11-08 15:48:53 [+0530], Shrikanth Hegde wrote:
>>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>>
>>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>>> return to kernel.
>>>
>>> Ran a few benchmarks and db workload on Power10. Performance is close to
>>> preempt=none/voluntary. It is possible that some patterns would
>>> differ in lazy[2]. More details of preempt lazy is here [1]
>>>
>>> Since Powerpc system can have large core count and large memory,
>>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>>
>>> [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
>>> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/
>> 
>> The lazy bits are only in tip.
>
> Hi Michael, I sent it to powerpc tree since all the changes were in 
> arch/powerpc. Please let me know if i have send it to tip tree instead.

I think I'd like it to have a full cycle of testing in next before going
into mainline. So I'll plan to take this via the powerpc tree for the
next cycle.

I assume you haven't tested 32-bit at all?

cheers

Re: [PATCH] powerpc: Add preempt lazy support

[Shrikanth Hegde]

On 11/14/24 07:31, Michael Ellerman wrote:
> Shrikanth Hegde <sshegde@linux.ibm.com> writes:
>> Thank you Sebastian for taking a look and rwb tag.
>>
>>> On 2024-11-08 15:48:53 [+0530], Shrikanth Hegde wrote:
>>>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>>>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>>>
>>>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>>>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>>>> return to kernel.
>>>>
>>>> Ran a few benchmarks and db workload on Power10. Performance is close to
>>>> preempt=none/voluntary. It is possible that some patterns would
>>>> differ in lazy[2]. More details of preempt lazy is here [1]
>>>>
>>>> Since Powerpc system can have large core count and large memory,
>>>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>>>
>>>> [1]: https://lore.kernel.org/lkml/20241007074609.447006177@infradead.org/
>>>> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-e4b93eb077b8@linux.ibm.com/
>>>
>>> The lazy bits are only in tip.
>>

I have added change suggested by sebastian. I think it makes sense since 
the large user copy using vmx could take sometime and in preemptible 
kernel it needs to resched as soon as possible. However i am not making 
it consider lazy since it would lead to quite a bit of context switches 
which is not necessary.

-       if (IS_ENABLED(CONFIG_PREEMPT) && need_resched())
+       if (IS_ENABLED(CONFIG_PREEMPTION) && need_resched())
                 set_dec(1);
         return 0;


>> Hi Michael, I sent it to powerpc tree since all the changes were in
>> arch/powerpc. Please let me know if i have send it to tip tree instead.
> 
> I think I'd like it to have a full cycle of testing in next before going
> into mainline. So I'll plan to take this via the powerpc tree for the
> next cycle.
> 

Make sense.

> I assume you haven't tested 32-bit at all?
>

Yes, 32 bit isn't tested.  it would be better if it goes through  a test 
cycle. I will send out v2 soon.

> cheers

Re: [PATCH] powerpc: Add preempt lazy support

[Shrikanth Hegde]

On 11/9/24 22:24, Shrikanth Hegde wrote:
> 
> 
> On 11/9/24 00:36, Ankur Arora wrote:
>>
>> Shrikanth Hegde <sshegde@linux.ibm.com> writes:
>>
>>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>>
>>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>>> return to kernel.
>>>
>>> Ran a few benchmarks and db workload on Power10. Performance is close to
>>> preempt=none/voluntary. It is possible that some patterns would
>>> differ in lazy[2]. More details of preempt lazy is here [1]
>>>
>>> Since Powerpc system can have large core count and large memory,
>>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>>
>>> [1]: https://lore.kernel.org/ 
>>> lkml/20241007074609.447006177@infradead.org/
>>> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b- 
>>> e4b93eb077b8@linux.ibm.com/
>>>
>>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>>
>> Looks good. Reviewed-by: <ankur.a.arora@oracle.com>
> 
> Thank you Ankur for taking a look and rwb tag.
> 
>>
>> However, I just checked and powerpc does not have
>> CONFIG_KVM_XFER_TO_GUEST_WORK. Do you need this additional patch
>> for handling the lazy bit at KVM guest entry?
> 

It doesn't use the generic kvm entry/exit either AFAIK. I need to 
understand more of this kvm maze. There are quite a lot of combinations.

> will take a look. Thanks for the pointers.
> 
>>
>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> index f14329989e9a..7bdf7015bb65 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -84,7 +84,8 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>>          hard_irq_disable();
>>
>>          while (true) {
>> -               if (need_resched()) {
>> +               unsigned long tf = read_thread_flags();
>> +               if (tf & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
>>                          local_irq_enable();
>>                          cond_resched();
>>                          hard_irq_disable();
>>

This is not going help since, with LAZY, cond_resched is nop. So it 
doesn't call to schedule. Same is true with preempt=full. I need to 
figure out if kvm stuff was tested for preempt=full.

Instead of cond_resched this needs to use schedule instead. Need to test 
it out and also see other places for kvm.
So, i need to spend more time on this and figure out, will send the 
patches after that.

>>
>> Ankur
> 

Re: [PATCH] powerpc: Add preempt lazy support

[Ankur Arora]

Shrikanth Hegde <sshegde@linux.ibm.com> writes:

> On 11/9/24 22:24, Shrikanth Hegde wrote:
>>
>> On 11/9/24 00:36, Ankur Arora wrote:
>>>
>>> Shrikanth Hegde <sshegde@linux.ibm.com> writes:
>>>
>>>> Define preempt lazy bit for Powerpc. Use bit 9 which is free and within
>>>> 16 bit range of NEED_RESCHED, so compiler can issue single andi.
>>>>
>>>> Since Powerpc doesn't use the generic entry/exit, add lazy check at exit
>>>> to user. CONFIG_PREEMPTION is defined for lazy/full/rt so use it for
>>>> return to kernel.
>>>>
>>>> Ran a few benchmarks and db workload on Power10. Performance is close to
>>>> preempt=none/voluntary. It is possible that some patterns would
>>>> differ in lazy[2]. More details of preempt lazy is here [1]
>>>>
>>>> Since Powerpc system can have large core count and large memory,
>>>> preempt lazy is going to be helpful in avoiding soft lockup issues.
>>>>
>>>> [1]: https://lore.kernel.org/ lkml/20241007074609.447006177@infradead.org/
>>>> [2]: https://lore.kernel.org/all/1a973dda-c79e-4d95-935b-
>>>> e4b93eb077b8@linux.ibm.com/
>>>>
>>>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>>>
>>> Looks good. Reviewed-by: <ankur.a.arora@oracle.com>
>> Thank you Ankur for taking a look and rwb tag.
>>
>>>
>>> However, I just checked and powerpc does not have
>>> CONFIG_KVM_XFER_TO_GUEST_WORK. Do you need this additional patch
>>> for handling the lazy bit at KVM guest entry?
>>
>
> It doesn't use the generic kvm entry/exit either AFAIK. I need to understand
> more of this kvm maze. There are quite a lot of combinations.

The generic kvm entry/exit is gated by CONFIG_KVM_XFER_TO_GUEST_WORK.

>> will take a look. Thanks for the pointers.
>>
>>>
>>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>>> index f14329989e9a..7bdf7015bb65 100644
>>> --- a/arch/powerpc/kvm/powerpc.c
>>> +++ b/arch/powerpc/kvm/powerpc.c
>>> @@ -84,7 +84,8 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>>>          hard_irq_disable();
>>>
>>>          while (true) {
>>> -               if (need_resched()) {
>>> +               unsigned long tf = read_thread_flags();
>>> +               if (tf & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {
>>>                          local_irq_enable();
>>>                          cond_resched();
>>>                          hard_irq_disable();
>>>
>
> This is not going help since, with LAZY, cond_resched is nop. So it doesn't call
> to schedule. Same is true with preempt=full. I need to figure out if kvm stuff
> was tested for preempt=full.
>
> Instead of cond_resched this needs to use schedule instead. Need to test it out
> and also see other places for kvm.

Oh yeah. Missed that it was calling cond_resched().

> So, i need to spend more time on this and figure out, will send the patches
> after that.
>
>>>
>>> Ankur
>>


--
ankur