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Message-ID: <e82ae909-5c40-4c8c-887a-a1e0d0cfe448@amd.com>
Date: Mon, 19 Aug 2024 10:49:22 -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 v6 09/22] x86/resctrl: Introduce MBM counters bitmap
Hi Reinette,
On 8/16/24 16:35, Reinette Chatre wrote:
> Hi Babu,
>
> On 8/6/24 3:00 PM, Babu Moger wrote:
>> Hardware provides a set of counters when mbm_cntr_assignable feature is
>> supported. These counters are used for assigning the events in resctrl
>> group when the feature is enabled.
>
> "in resctrl group" -> "in a resctrl group"?
>
Sure.
>>
>> Introduce mbm_cntrs_free_map bitmap to track available and free counters
>
> What is the difference between an available and a free counter?
It is the same. Will correct the text here.
>
>> and set of routines to allocate and free the counters.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>
>> ---
>> arch/x86/kernel/cpu/resctrl/internal.h | 2 ++
>> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 33 ++++++++++++++++++++++++++
>> 2 files changed, 35 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
>> b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 154983a67646..6263362496a3 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -662,6 +662,8 @@ void __check_limbo(struct rdt_mon_domain *d, bool
>> force_free);
>> void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
>> void __init resctrl_file_fflags_init(const char *config,
>> unsigned long fflags);
>> +int mbm_cntr_alloc(struct rdt_resource *r);
>> +void mbm_cntr_free(u32 cntr_id);
>> 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 ab4fab3b7cf1..c818965e36c9 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -185,6 +185,37 @@ bool closid_allocated(unsigned int closid)
>> return !test_bit(closid, &closid_free_map);
>> }
>> +/*
>> + * Counter bitmap for tracking the available counters.
>> + * ABMC feature provides set of hardware counters for enabling events.
>
> "ABMC feature" -> "mbm_cntr_assign mode"
Sure.
>
>> + * Each event takes one hardware counter. Kernel needs to keep track
>
> "Each event takes one hardware counter" -> "Each RMID and event pair takes
> one hardware counter" ?
Sure.
>
>
>> + * of number of available counters.
>
> "of number of available counters" -> "of the number of available counters"?
Sure.
>
>> + */
>> +static DECLARE_BITMAP(mbm_cntrs_free_map, 64);
>> +
>> +static void mbm_cntrs_init(struct rdt_resource *r)
>> +{
>> + bitmap_fill(mbm_cntrs_free_map, r->mon.num_mbm_cntrs);
>
> Apart from what James mentioned about the different sizes, please also
> add checking that the resource actually supports monitoring and
> assignable counters before proceeding with the bitmap ops.
Sure.
>
>> +}
>> +
>> +int mbm_cntr_alloc(struct rdt_resource *r)
>> +{
>> + int cntr_id;
>> +
>> + cntr_id = find_first_bit(mbm_cntrs_free_map, r->mon.num_mbm_cntrs);
>> + if (cntr_id >= r->mon.num_mbm_cntrs)
>> + return -ENOSPC;
>> +
>> + __clear_bit(cntr_id, mbm_cntrs_free_map);
>> +
>> + return cntr_id;
>> +}
>> +
>> +void mbm_cntr_free(u32 cntr_id)
>> +{
>> + __set_bit(cntr_id, mbm_cntrs_free_map);
>> +}
>> +
>> /**
>> * rdtgroup_mode_by_closid - Return mode of resource group with closid
>> * @closid: closid if the resource group
>> @@ -2748,6 +2779,8 @@ static int rdt_get_tree(struct fs_context *fc)
>> closid_init();
>> + mbm_cntrs_init(&rdt_resources_all[RDT_RESOURCE_L3].r_resctrl);
>> +
>> if (resctrl_arch_mon_capable())
>> flags |= RFTYPE_MON;
>>
>
> This is also an example of what James mentioned elsewhere where there is an
> assumption that this feature applies to the L3 resource. This has a
> consequence
> that some code is global (like mbm_cntrs_free_map), assuming the L3
> resource, while
> other code takes the resource as parameter (eg. mbm_cntr_alloc()). This
> results
> in inconsistent interface where, for example, allocating a counter needs
Yes. Will address it.
> resource
> as parameter but freeing a counter does not. James already proposed different
> treatment of the bitmap and L3 resource parameters, I expect with such
> guidance
> the interfaces will become more intuitive.
>
How about making "mbm_cntrs_free_map" as part of struct resctrl_mon?
It will be pointer and allocated dynamically based on number of counters.
All the related information (num_mbm_cntrs and mbm_cntr_assignable) is
already part of this data structure.
--
Thanks
Babu Moger
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