linux-kernel - Re: [PATCH v3 3/4] powerpc/watchdog: introduce a NMI watchdog's factor

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Message-ID: <b92a58db-7fe3-fa88-329e-953ef4b7ebbd@linux.ibm.com>
Date:   Tue, 12 Jul 2022 11:51:37 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>, benh@...nel.crashing.org,
        haren@...ux.vnet.ibm.com, linux@...ck-us.net, mpe@...erman.id.au,
        nathanl@...ux.ibm.com, paulus@...ba.org, wim@...ux-watchdog.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v3 3/4] powerpc/watchdog: introduce a NMI watchdog's
 factor

Le 12/07/2022 à 03:42, Nicholas Piggin a écrit :
> Excerpts from Laurent Dufour's message of June 27, 2022 11:53 pm:
>> Introduce a factor which would apply to the NMI watchdog timeout.
>>
>> This factor is a percentage added to the watchdog_tresh value. The value is
>> set under the watchdog_mutex protection and lockup_detector_reconfigure()
>> is called to recompute wd_panic_timeout_tb.
>>
>> Once the factor is set, it remains until it is set back to 0, which means
>> no impact.
> 
> Looks okay. We could worry about making it more generic or nicer if
> another user came along.
> 
> Could you make the naming a bit more self documenting? 
> watchdog_nmi_set_timeout_pct(), maybe? Does the wd really care
> that it is for LPM in particular?

You're right, the name should not mention lpm.
For my information, what does "pct" stand for?

> 
> Variables and parameters could have a _pct suffix too.

I'll do that.

> 
> Otherwise
> 
> Reviewed-by: Nicholas Piggin <npiggin@...il.com>
> 
>>
>> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
>> ---
>>  arch/powerpc/include/asm/nmi.h |  2 ++
>>  arch/powerpc/kernel/watchdog.c | 21 ++++++++++++++++++++-
>>  2 files changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/nmi.h b/arch/powerpc/include/asm/nmi.h
>> index ea0e487f87b1..7d6a8d9b0543 100644
>> --- a/arch/powerpc/include/asm/nmi.h
>> +++ b/arch/powerpc/include/asm/nmi.h
>> @@ -5,8 +5,10 @@
>>  #ifdef CONFIG_PPC_WATCHDOG
>>  extern void arch_touch_nmi_watchdog(void);
>>  long soft_nmi_interrupt(struct pt_regs *regs);
>> +void watchdog_nmi_set_lpm_factor(u64 factor);
>>  #else
>>  static inline void arch_touch_nmi_watchdog(void) {}
>> +static inline void watchdog_nmi_set_lpm_factor(u64 factor) {}
>>  #endif
>>  
>>  #ifdef CONFIG_NMI_IPI
>> diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
>> index 7d28b9553654..80851b228f71 100644
>> --- a/arch/powerpc/kernel/watchdog.c
>> +++ b/arch/powerpc/kernel/watchdog.c
>> @@ -91,6 +91,10 @@ static cpumask_t wd_smp_cpus_pending;
>>  static cpumask_t wd_smp_cpus_stuck;
>>  static u64 wd_smp_last_reset_tb;
>>  
>> +#ifdef CONFIG_PPC_PSERIES
>> +static u64 wd_factor;
>> +#endif
>> +
>>  /*
>>   * Try to take the exclusive watchdog action / NMI IPI / printing lock.
>>   * wd_smp_lock must be held. If this fails, we should return and wait
>> @@ -527,7 +531,13 @@ static int stop_watchdog_on_cpu(unsigned int cpu)
>>  
>>  static void watchdog_calc_timeouts(void)
>>  {
>> -	wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq;
>> +	u64 threshold = watchdog_thresh;
>> +
>> +#ifdef CONFIG_PPC_PSERIES
>> +	threshold += (READ_ONCE(wd_factor) * threshold) / 100;
>> +#endif
>> +
>> +	wd_panic_timeout_tb = threshold * ppc_tb_freq;
>>  
>>  	/* Have the SMP detector trigger a bit later */
>>  	wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2;
>> @@ -570,3 +580,12 @@ int __init watchdog_nmi_probe(void)
>>  	}
>>  	return 0;
>>  }
>> +
>> +#ifdef CONFIG_PPC_PSERIES
>> +void watchdog_nmi_set_lpm_factor(u64 factor)
>> +{
>> +	pr_info("Set the NMI watchdog factor to %llu%%\n", factor);
>> +	WRITE_ONCE(wd_factor, factor);
>> +	lockup_detector_reconfigure();
>> +}
>> +#endif
>> -- 
>> 2.36.1
>>
>>