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Date:   Fri, 28 Jul 2023 17:29:40 +0100
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Subject: Re: [PATCH v4 21/24] x86/resctrl: Allow overflow/limbo handlers to be
 scheduled on any-but cpu
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To:     "Shaopeng Tan (Fujitsu)" <tan.shaopeng@fujitsu.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc:     Fenghua Yu <fenghua.yu@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        Babu Moger <Babu.Moger@amd.com>,
        "shameerali.kolothum.thodi@huawei.com" 
        <shameerali.kolothum.thodi@huawei.com>,
        D Scott Phillips OS <scott@os.amperecomputing.com>,
        "carl@os.amperecomputing.com" <carl@os.amperecomputing.com>,
        "lcherian@marvell.com" <lcherian@marvell.com>,
        "bobo.shaobowang@huawei.com" <bobo.shaobowang@huawei.com>,
        "xingxin.hx@openanolis.org" <xingxin.hx@openanolis.org>,
        "baolin.wang@linux.alibaba.com" <baolin.wang@linux.alibaba.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Xin Hao <xhao@linux.alibaba.com>,
        "peternewman@google.com" <peternewman@google.com>,
        "dfustini@baylibre.com" <dfustini@baylibre.com>
References: <20230525180209.19497-1-james.morse@arm.com>
 <20230525180209.19497-22-james.morse@arm.com>
 <TYAPR01MB63307451E66EBDB7F885F13D8B51A@TYAPR01MB6330.jpnprd01.prod.outlook.com>
From:   James Morse <james.morse@arm.com>
In-Reply-To: <TYAPR01MB63307451E66EBDB7F885F13D8B51A@TYAPR01MB6330.jpnprd01.prod.outlook.com>
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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