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

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Message-ID: <6513da1c-ae84-14a3-1e95-30704e1162a4@arm.com>
Date:   Fri, 28 Jul 2023 17:29:40 +0100
From:   James Morse <james.morse@....com>
To:     "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        "carl@...amperecomputing.com" <carl@...amperecomputing.com>,
        "lcherian@...vell.com" <lcherian@...vell.com>,
        "bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
        "xingxin.hx@...nanolis.org" <xingxin.hx@...nanolis.org>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>,
        "peternewman@...gle.com" <peternewman@...gle.com>,
        "dfustini@...libre.com" <dfustini@...libre.com>
Subject: Re: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be
 scheduled on any-but cpu

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