linux-kernel - Re: [PATCH v3 1/1] powerpc: Enable dynamic preemption

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Message-ID: <05f6f732-e155-4b60-8c4e-984e42e51ee4@csgroup.eu>
Date: Thu, 30 Jan 2025 16:03:09 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: mpe@...erman.id.au, maddy@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org,
 npiggin@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] powerpc: Enable dynamic preemption



Le 30/01/2025 à 15:54, Sebastian Andrzej Siewior a écrit :
> On 2025-01-06 10:49:19 [+0530], Shrikanth Hegde wrote:
>> --- a/arch/powerpc/kernel/interrupt.c
>> +++ b/arch/powerpc/kernel/interrupt.c
>> @@ -25,6 +25,10 @@
>>   unsigned long global_dbcr0[NR_CPUS];
>>   #endif
>>   
>> +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
>> +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
>> +#endif
> 
> I am uncertain here: Do you need to DEFINE it? It is set by the sched
> core which also defines it. It should be same thing after all, right?

As far as I can see it is not handled by sched core.

$ git grep sk_dynamic_irqentry_exit_cond_resched
arch/arm64/include/asm/preempt.h:DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
arch/arm64/kernel/entry-common.c:DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
arch/arm64/kernel/entry-common.c: 
(static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
include/linux/entry-common.h:DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
kernel/entry/common.c:DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
kernel/entry/common.c:  if 
(!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))

It is in common entry but arm64 and powerpc don't use common entry.

$ git grep GENERIC_ENTRY arch
arch/Kconfig:config GENERIC_ENTRY
arch/loongarch/Kconfig: select GENERIC_ENTRY
arch/riscv/Kconfig:     select GENERIC_ENTRY
arch/s390/Kconfig:      select GENERIC_ENTRY
arch/x86/Kconfig:       select GENERIC_ENTRY


Christophe