linux-kernel - Re: [PATCH v6 16/22] x86/resctrl: Add the interface to unassign a MBM counter

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Message-ID: <5e1426cf-f966-447c-8455-88b70ab324d9@intel.com>
Date: Fri, 23 Aug 2024 13:18:35 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....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 v6 16/22] x86/resctrl: Add the interface to unassign a MBM
 counter

Hi Babu,

On 8/21/24 9:01 AM, Moger, Babu wrote:
> Hi Reinette,
> 
> On 8/16/24 16:41, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 8/6/24 3:00 PM, Babu Moger wrote:
>>> The ABMC feature provides an option to the user to assign a hardware
>>
>> This is about resctrl fs so "The ABMC feature" -> "mbm_cntr_assign mode"
> 
> Sure.
> 
>> (please check whole series).
> 
> Sure.
> 
>>
>>> counter to an RMID and monitor the bandwidth as long as it is assigned.
>>> The assigned RMID will be tracked by the hardware until the user unassigns
>>> it manually.
>>>
>>> Hardware provides only limited number of counters. If the system runs out
>>> of assignable counters, kernel will display an error when a new assignment
>>> is requested. Users need to unassign a already assigned counter to make
>>> space for new assignment.
>>>
>>> Provide the interface to unassign the counter ids from the group. Free the
>>> counter if it is not assigned in any of the domains.
>>>
>>> The feature details are documented in the APM listed below [1].
>>> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
>>>       Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable
>>> Bandwidth
>>>       Monitoring (ABMC).
>>>
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
>>> Signed-off-by: Babu Moger <babu.moger@....com>
>>> ---
>>> v6: Removed mbm_cntr_free from this patch.
>>>       Added counter test in all the domains and free if it is not
>>> assigned to
>>>       any domains.
>>>
>>> v5: Few name changes to match cntr_id.
>>>       Changed the function names to
>>>       rdtgroup_unassign_cntr
>>>       More comments on commit log.
>>>
>>> v4: Added domain specific unassign feature.
>>>       Few name changes.
>>>
>>> v3: Removed the static from the prototype of rdtgroup_unassign_abmc.
>>>       The function is not called directly from user anymore. These
>>>       changes are related to global assignment interface.
>>>
>>> v2: No changes.
>>> ---
>>>    arch/x86/kernel/cpu/resctrl/internal.h |  2 +
>>>    arch/x86/kernel/cpu/resctrl/rdtgroup.c | 52 ++++++++++++++++++++++++++
>>>    2 files changed, 54 insertions(+)
>>>
>>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
>>> b/arch/x86/kernel/cpu/resctrl/internal.h
>>> index 4e8109dee174..cc832955b787 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>>> @@ -689,6 +689,8 @@ int resctrl_arch_assign_cntr(struct rdt_mon_domain
>>> *d, enum resctrl_event_id evt
>>>                     u32 rmid, u32 cntr_id, u32 closid, bool assign);
>>>    int rdtgroup_assign_cntr(struct rdtgroup *rdtgrp, enum
>>> resctrl_event_id evtid);
>>>    int rdtgroup_alloc_cntr(struct rdtgroup *rdtgrp, int index);
>>> +int rdtgroup_unassign_cntr(struct rdtgroup *rdtgrp, enum
>>> resctrl_event_id evtid);
>>> +void rdtgroup_free_cntr(struct rdt_resource *r, struct rdtgroup
>>> *rdtgrp, int index);
>>>    void rdt_staged_configs_clear(void);
>>>    bool closid_allocated(unsigned int closid);
>>>    int resctrl_find_cleanest_closid(void);
>>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> index 1ee91a7293a8..0c2215dbd497 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> @@ -1961,6 +1961,58 @@ int rdtgroup_assign_cntr(struct rdtgroup *rdtgrp,
>>> enum resctrl_event_id evtid)
>>>        return 0;
>>>    }
>>>    +static int rdtgroup_mbm_cntr_test(struct rdt_resource *r, u32 cntr_id)
>>
>> Could "test" be replaced with something more specific about what is tested?
>> for example, "rdtgroup_mbm_cntr_is_assigned()" or something better? The
> 
> Yes. We can do that.
> 
>> function
>> looks like a good candidate for returning a bool.
> 
> Sure.
>>
>> Is this function needed though? (more below)
> 
> Yes. It is required. It is called from two places
> (rdtgroup_unassign_update and rdtgroup_unassign_cntr).
> 
> We can open code in rdtgroup_unassign_cntr. But we can't do that in
> rdtgroup_unassign_update. But, I will check again for sure.

Similar to rdtgroup_assign_cntr() and rdtgroup_assign_update() discussed
in previous patch, it also looks like rdtgroup_unassign_cntr() and
rdtgroup_unassign_update() can be merged.

Reinette