linux-kernel - Re: [PATCH v2 4/4] pseries/mobility: Set NMI watchdog factor during LPM

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Message-ID: <040a8f52-980f-146c-6811-9a0ce9157f08@linux.ibm.com>
Date:   Fri, 24 Jun 2022 16:09:34 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Nathan Lynch <nathanl@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        haren@...ux.vnet.ibm.com, npiggin@...il.com
Subject: Re: [PATCH v2 4/4] pseries/mobility: Set NMI watchdog factor during
 LPM

On 23/06/2022, 19:28:34, Nathan Lynch wrote:
> Laurent Dufour <ldufour@...ux.ibm.com> writes:
>> diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
>> index 179bbd4ae881..4284ceaf9060 100644
>> --- a/arch/powerpc/platforms/pseries/mobility.c
>> +++ b/arch/powerpc/platforms/pseries/mobility.c
>> @@ -48,6 +48,39 @@ struct update_props_workarea {
>>  #define MIGRATION_SCOPE	(1)
>>  #define PRRN_SCOPE -2
>>  
>> +#ifdef CONFIG_PPC_WATCHDOG
>> +static unsigned int lpm_nmi_wd_factor = 200;
>> +
>> +#ifdef CONFIG_SYSCTL
>> +static struct ctl_table lpm_nmi_wd_factor_ctl_table[] = {
>> +	{
>> +		.procname	= "lpm_nmi_watchdog_factor",
> 
> Assuming the basic idea is acceptable, I suggest making the user-visible
> name more generic (e.g. "nmi_watchdog_factor") in case it makes sense to
> apply this to other contexts in the future.

Fair enough, indeed, I was wondering if "lpm" is meaningful.

> 
>> +		.data		= &lpm_nmi_wd_factor,
>> +		.maxlen		= sizeof(int),
>> +		.mode		= 0644,
>> +		.proc_handler	= proc_douintvec_minmax,
>> +	},
>> +	{}
>> +};
>> +static struct ctl_table lpm_nmi_wd_factor_sysctl_root[] = {
>> +	{
>> +		.procname       = "kernel",
>> +		.mode           = 0555,
>> +		.child          = lpm_nmi_wd_factor_ctl_table,
>> +	},
>> +	{}
>> +};
>> +
>> +static int __init register_lpm_nmi_wd_factor_sysctl(void)
>> +{
>> +	register_sysctl_table(lpm_nmi_wd_factor_sysctl_root);
>> +
>> +	return 0;
>> +}
>> +device_initcall(register_lpm_nmi_wd_factor_sysctl);
>> +#endif /* CONFIG_SYSCTL */
>> +#endif /* CONFIG_PPC_WATCHDOG */
>> +
>>  static int mobility_rtas_call(int token, char *buf, s32 scope)
>>  {
>>  	int rc;
>> @@ -702,6 +735,7 @@ static int pseries_suspend(u64 handle)
>>  static int pseries_migrate_partition(u64 handle)
>>  {
>>  	int ret;
>> +	unsigned int factor = lpm_nmi_wd_factor;
>>  
>>  	ret = wait_for_vasi_session_suspending(handle);
>>  	if (ret)
>> @@ -709,6 +743,13 @@ static int pseries_migrate_partition(u64 handle)
>>  
>>  	vas_migration_handler(VAS_SUSPEND);
>>  
>> +#ifdef CONFIG_PPC_WATCHDOG
>> +	if (factor) {
>> +		pr_info("Set the NMI watchdog factor to %u%%\n", factor);
>> +		watchdog_nmi_set_lpm_factor(factor);
>> +	}
>> +#endif /* CONFIG_PPC_WATCHDOG */
>> +
>>  	ret = pseries_suspend(handle);
>>  	if (ret == 0) {
>>  		post_mobility_fixup();
>> @@ -716,6 +757,13 @@ static int pseries_migrate_partition(u64 handle)
>>  	} else
>>  		pseries_cancel_migration(handle, ret);
>>  
>> +#ifdef CONFIG_PPC_WATCHDOG
>> +	if (factor) {
>> +		pr_info("Restoring NMI watchdog timer\n");
>> +		watchdog_nmi_set_lpm_factor(0);
>> +	}
>> +#endif /* CONFIG_PPC_WATCHDOG */
>> +
> 
> A couple more suggestions:
> 
> * Move the prints into a single statement in watchdog_nmi_set_lpm_factor().

You're right that sounds a better place.

> 
> * Add no-op versions of watchdog_nmi_set_lpm_factor for
>   !CONFIG_PPC_WATCHDOG so we can minimize the #ifdef here.
>

Furthermore, this breaks compilation when !CONFIG_PPC_WATCHDOG because
lpm_nmi_wd_factor is not defined. I'll rework that part.

> Otherwise this looks fine to me.

Thanks,
Laurent.