linux-kernel - Re: [PATCH v4 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid

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Date:   Fri, 28 Jul 2023 17:34:29 +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 15/24] x86/resctrl: Allow arch to allocate memory
 needed in resctrl_arch_rmid_read()

Hi Shaopeng TAN,

On 12/06/2023 06:39, Shaopeng Tan (Fujitsu) wrote:
>> Depending on the number of monitors available, Arm's MPAM may need to
>> allocate a monitor prior to reading the counter value. Allocating a contended
>> resource may involve sleeping.
>>
>> add_rmid_to_limbo() calls resctrl_arch_rmid_read() for multiple domains, the
>> allocation should be valid for all domains.
>>
>> __check_limbo() and mon_event_count() each make multiple calls to
>> resctrl_arch_rmid_read(), to avoid extra work on contended systems, the
>> allocation should be valid for multiple invocations of resctrl_arch_rmid_read().
>>
>> Add arch hooks for this allocation, which need calling before
>> resctrl_arch_rmid_read(). The allocated monitor is passed to
>> resctrl_arch_rmid_read(), then freed again afterwards. The helper can be
>> called on any CPU, and can sleep.

>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index fb33100e172b..6d140018358a 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c

>> @@ -331,9 +331,14 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
>>  	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>>  	struct rmid_entry *entry;
>>  	u32 idx, cur_idx = 1;
>> +	void *arch_mon_ctx;
>>  	bool rmid_dirty;
>>  	u64 val = 0;
>>
>> +	arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r,
>> QOS_L3_OCCUP_EVENT_ID);
>> +	if (arch_mon_ctx < 0)
>> +		return;
>> +
> 
> Would it be better to use IS_ERR() macro?

Yup, much more readable!


Thanks,

James