linux-kernel - Re: [PATCH v11 10/23] x86/resctrl: Remove MSR reading of event configuration value

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Message-ID: <ffb74a45-ca63-46a4-9047-d55c9f51375a@intel.com>
Date: Thu, 6 Feb 2025 08:17:41 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Xin Li <xin@...or.com>, Babu Moger <babu.moger@....com>, <corbet@....net>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <tony.luck@...el.com>,
	<peternewman@...gle.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<akpm@...ux-foundation.org>, <thuth@...hat.com>, <rostedt@...dmis.org>,
	<xiongwei.song@...driver.com>, <pawan.kumar.gupta@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <jpoimboe@...nel.org>,
	<perry.yuan@....com>, <sandipan.das@....com>, <kai.huang@...el.com>,
	<xiaoyao.li@...el.com>, <seanjc@...gle.com>, <xin3.li@...el.com>,
	<andrew.cooper3@...rix.com>, <ebiggers@...gle.com>,
	<mario.limonciello@....com>, <james.morse@....com>,
	<tan.shaopeng@...itsu.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <maciej.wieczor-retman@...el.com>,
	<eranian@...gle.com>
Subject: Re: [PATCH v11 10/23] x86/resctrl: Remove MSR reading of event
 configuration value

Hi Xin,

On 2/5/25 10:24 PM, Xin Li wrote:
> On 1/22/2025 12:20 PM, Babu Moger wrote:
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 8917c7261680..6fe9e610e9a0 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1324,3 +1324,49 @@ int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable)
>>         return 0;
>>   }
>> +
>> +u32 resctrl_arch_mon_event_config_get(struct rdt_mon_domain *d,
>> +                      enum resctrl_event_id eventid)
>> +{
>> +    struct rdt_hw_mon_domain *hw_dom = resctrl_to_arch_mon_dom(d);
>> +
>> +    switch (eventid) {
>> +    case QOS_L3_OCCUP_EVENT_ID:
>> +        break;
>> +    case QOS_L3_MBM_TOTAL_EVENT_ID:
>> +        return hw_dom->mbm_total_cfg;
>> +    case QOS_L3_MBM_LOCAL_EVENT_ID:
>> +        return hw_dom->mbm_local_cfg;
>> +    }
>> +
>> +    /* Never expect to get here */
>> +    WARN_ON_ONCE(1);
>> +
>> +    return INVALID_CONFIG_VALUE;
>> +}
>> +
>> +void resctrl_arch_mon_event_config_set(void *info)
>> +{
>> +    struct mon_config_info *mon_info = info;
>> +    struct rdt_hw_mon_domain *hw_dom;
>> +    unsigned int index;
>> +
>> +    index = mon_event_config_index_get(mon_info->evtid);
>> +    if (index == INVALID_CONFIG_INDEX)
>> +        return;
>> +
>> +    wrmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, 0);
> 
> This is the existing code, however it would be better to use wrmsrl()
> when the higher 32-bit are all 0s:
> 
>     wrmsrl(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config);
> 

Could you please elaborate what makes this change better?

Thank you!

Reinette