Re: [PATCH 7/7] powerpc: add support for PREEMPT_LAZY

[Ankur Arora]

Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> writes:

> On 2024-10-09 09:54:11 [-0700], Ankur Arora wrote:
>> From: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
>>
>> Add PowerPC arch support for PREEMPT_LAZY by defining LAZY bits.
>>
>> Since PowerPC doesn't use generic exit to functions, check for
>> NEED_RESCHED_LAZY when exiting to user or to the kernel from
>> interrupt routines.
>>
>> Signed-off-by: Shrikanth Hegde <sshegde@xxxxxxxxxxxxx>
>> [ Changed TIF_NEED_RESCHED_LAZY to now be defined unconditionally. ]
>> Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
>> ---
>>  arch/powerpc/Kconfig                   | 1 +
>>  arch/powerpc/include/asm/thread_info.h | 5 ++++-
>>  arch/powerpc/kernel/interrupt.c        | 5 +++--
>>  3 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 8094a01974cc..593a1d60d443 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -270,6 +270,7 @@ config PPC
>>  	select HAVE_PERF_REGS
>>  	select HAVE_PERF_USER_STACK_DUMP
>>  	select HAVE_RETHOOK			if KPROBES
>> +	select ARCH_HAS_PREEMPT_LAZY
>>  	select HAVE_REGS_AND_STACK_ACCESS_API
>>  	select HAVE_RELIABLE_STACKTRACE
>>  	select HAVE_RSEQ
>
> I would move this up to the ARCH_HAS_ block.

Makes sense.

>> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
>> index 6ebca2996f18..ae7793dae763 100644
>> --- a/arch/powerpc/include/asm/thread_info.h
>> +++ b/arch/powerpc/include/asm/thread_info.h
>> @@ -117,11 +117,14 @@ void arch_setup_new_exec(void);
>>  #endif
>>  #define TIF_POLLING_NRFLAG	19	/* true if poll_idle() is polling TIF_NEED_RESCHED */
>>  #define TIF_32BIT		20	/* 32 bit binary */
>> +#define TIF_NEED_RESCHED_LAZY	21	/* Lazy rescheduling */
>
> I don't see any of the bits being used in assembly anymore.
> If you group the _TIF_USER_WORK_MASK bits it a single 16 bit block then
> the compiler could issue a single andi.

I don't know power asm at all, but this seems like a good idea.

Shrikanth?

--
ankur