Re: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu

[James Morse <james.morse@arm.com>]

Hi Shaopeng Tan,

On 09/06/2023 12:10, Shaopeng Tan (Fujitsu) wrote:
>> When a CPU is taken offline resctrl may need to move the overflow or limbo
>> handlers to run on a different CPU.
>>
>> Once the offline callbacks have been split, cqm_setup_limbo_handler() will be
>> called while the CPU that is going offline is still present in the cpu_mask.
>>
>> Pass the CPU to exclude to cqm_setup_limbo_handler() and
>> mbm_setup_overflow_handler(). These functions can use a variant of
>> cpumask_any_but() when selecting the CPU. -1 is used to indicate no CPUs
>> need excluding.
>>
>> A subsequent patch moves these calls to be before CPUs have been removed,
>> so this exclude_cpus behaviour is temporary.

>> diff --git
>> a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index ced933694f60..ae02185f3354 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -875,9 +895,15 @@ void mbm_setup_overflow_handler(struct rdt_domain
>> *dom, unsigned long delay_ms)
>>  	 */
>>  	if (!resctrl_mounted || !resctrl_arch_mon_capable())
>>  		return;
>> -	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>> +	if (exclude_cpu == -1)
>> +		cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> 
> Should RESCTRL_PICK_ANY_CPU be used instead of -1?

Yup, that would be more readable. I did this for cqm_setup_limbo_handler(), but for some
reason missed this one.


Thanks,

James