linux-kernel - Re: [PATCH v4 17/19] x86/resctrl: Introduce the interface switch between ABMC and mbm

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Date: Thu, 20 Jun 2024 09:53:26 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 fenghua.yu@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
 tj@...nel.org, peterz@...radead.org, yanjiewtw@...il.com,
 kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
 jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
 rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
 jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v4 17/19] x86/resctrl: Introduce the interface switch
 between ABMC and mbm_legacy

Hi Reinette,

On 6/13/24 20:51, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/24/24 5:23 AM, Babu Moger wrote:
>> Introduce interface to switch between ABMC and legacy_mbm modes.
> 
> shortlog and first sentence of changelog do not match: mbm_legacy vs
> legacy_mbm?

Will correct it.

> 
>>
>> By default ABMC is enabled on resctrl mount if the feature is available.
>> However, user will have the option to go back to legacy_mbm if required.
>>
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign
>> [abmc]
>> mbm_legacy
>>
>> To enable the legacy monitoring feature:
>> $ echo  "mbm_legacy" > /sys/fs/resctrl/info/L3_MON/mbm_assign
> 
> Missing information about user visible impact to counters/events
> and any mitigations needed in implementation.

Sure. Will add the details.

> 
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v4: Minor commit text changes. Keep the default to ABMC when supported.
>>
>> v3: New patch to address the review comments from upstream.
>> ---
>>   Documentation/arch/x86/resctrl.rst     | 10 +++++++
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 40 +++++++++++++++++++++++++-
>>   2 files changed, 49 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst
>> b/Documentation/arch/x86/resctrl.rst
>> index ab3cde61a124..fd050d4d22cd 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -271,6 +271,16 @@ with the following files:
>>         [abmc]
>>         mbm_legacy
>>   +    * To enable ABMC feature:
>> +      ::
>> +
>> +        # echo  "abmc" > /sys/fs/resctrl/info/L3_MON/mbm_assign
>> +
>> +    * To enable the legacy monitoring feature:
>> +      ::
>> +
>> +        # echo  "mbm_legacy" > /sys/fs/resctrl/info/L3_MON/mbm_assign
>> +
> 
> No information about what the features are or what will happen on such a
> switch.

Ok. Sure.  Will add more documentation.

> 
>>   "max_threshold_occupancy":
>>           Read/write file provides the largest value (in
>>           bytes) at which a previously used LLC_occupancy
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index f452b6d9bb99..d77ff059269a 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -908,6 +908,43 @@ static int rdtgroup_mbm_assign_show(struct
>> kernfs_open_file *of,
>>       return 0;
>>   }
>>   +/*
>> + * rdtgroup_mode_write - Modify the resource group's mode
> 
> Comment does not match function name. Seems like "mode" is the generic term
> to use instead of "assign".

Sure. Will fix.

> 
>> + */
>> +static ssize_t rdtgroup_mbm_assign_write(struct kernfs_open_file *of,
>> +                     char *buf, size_t nbytes,
>> +                     loff_t off)
>> +{
>> +    struct rdt_resource *r = of->kn->parent->priv;
>> +    int ret = 0;
>> +
>> +    if (!r->abmc_capable)
>> +        return -EINVAL;
>> +
>> +    /* Valid input requires a trailing newline */
>> +    if (nbytes == 0 || buf[nbytes - 1] != '\n')
>> +        return -EINVAL;
>> +
>> +    buf[nbytes - 1] = '\0';
>> +
>> +    cpus_read_lock();
>> +    mutex_lock(&rdtgroup_mutex);
>> +
>> +    rdt_last_cmd_clear();
>> +
>> +    if (!strcmp(buf, "mbm_legacy"))
>> +        resctrl_abmc_disable(RDT_RESOURCE_L3);
>> +    else if (!strcmp(buf, "abmc"))
>> +        ret = resctrl_abmc_enable(RDT_RESOURCE_L3);
>> +    else
>> +        ret = -EINVAL;
>> +
>> +    mutex_unlock(&rdtgroup_mutex);
>> +    cpus_read_unlock();
>> +
>> +    return ret ?: nbytes;
>> +}
>> +
>>   #ifdef CONFIG_PROC_CPU_RESCTRL
>>     /*
>> @@ -2087,9 +2124,10 @@ static struct rftype res_common_files[] = {
>>       },
>>       {
>>           .name        = "mbm_assign",
>> -        .mode        = 0444,
>> +        .mode        = 0644,
>>           .kf_ops        = &rdtgroup_kf_single_ops,
>>           .seq_show    = rdtgroup_mbm_assign_show,
>> +        .write        = rdtgroup_mbm_assign_write,
>>       },
>>       {
>>           .name        = "cpus",
> 
> 
> Reinette
> 

-- 
Thanks
Babu Moger