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

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Message-Id: <1657589870.vvurapsif3.astroid@bobo.none>
Date:   Tue, 12 Jul 2022 11:42:52 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     benh@...nel.crashing.org, haren@...ux.vnet.ibm.com,
        Laurent Dufour <ldufour@...ux.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

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?

Variables and parameters could have a _pct suffix too.

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
> 
>