Message-ID: <16b7768c-8f68-65fb-19a5-55a117dd0603@amd.com>
Date: Wed, 19 Jun 2024 17:38:19 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <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 v4 14/19] x86/resctrl: Add the interface to assign ABMC
 counter

Hi Reinette,

On 6/13/2024 8:48 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/24/24 5:23 AM, Babu Moger wrote:
>> ABMC feature requires to users to assign a hardware counter to an RMID
> 
> "requires to users" -> "requires users"?

Sure.

> 
>> to monitor the events. Provide the interfaces to assign a counter.
>>
>> Individual counters are configured by writing to L3_QOS_ABMC_CFG MSR
>> and specifying the counter id, bandwidth source, and bandwidth types.
> 
> Where is discription of what this patch does and why?
> 
> This and following patches seem to introduce building blocks that
> are only used later in series. These building blocks are introduced
> without any information about what they do and why and that makes it
> difficult to understand how this work will fall into place.

Ok. Will elaborate this.


> 
>>
>> 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).
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
>> ---
>> v4: Commit message update.
>>      User bitmap APIs where applicable.
>>      Changed the interfaces considering MPAM(arm).
>>      Added domain specific assignment.
>>
>> v3: Removed the static from the prototype of rdtgroup_assign_abmc.
>>      The function is not called directly from user anymore. These
>>      changes are related to global assignment interface.
>>
>> v2: Minor text changes in commit message.
>> ---
>>   arch/x86/kernel/cpu/resctrl/internal.h |   3 +
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 101 +++++++++++++++++++++++++
>>   2 files changed, 104 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h 
>> b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 45ed33f4f0ff..a88c8fc5e4df 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -657,6 +657,9 @@ void rdt_domain_reconfigure_cdp(struct 
>> rdt_resource *r);
>>   void __init resctrl_file_fflags_init(const char *config,
>>                        unsigned long fflags);
>>   void arch_domain_mbm_evt_config(struct rdt_hw_domain *hw_dom);
>> +int resctrl_arch_assign(struct rdt_domain *d, u32 evtid, u32 rmid,
>> +            u32 ctr_id, u32 closid, bool enable);
>> +int resctrl_grp_assign(struct rdtgroup *rdtgrp, u32 evtid);
>>   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 0e425c91fa46..48df76499a04 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -203,6 +203,19 @@ static void num_cntrs_init(void)
>>       num_cntrs_free_map_len = r->mon.num_cntrs;
>>   }
>> +static int assign_cntrs_alloc(void)
> 
> Only one counter is allocated and "assign" is unexpected since it
> seems to imply how this counter will be used.
> It can just be "mon_cntr_alloc()"?

Sure.

> 
>> +{
>> +    u32 ctr_id = find_first_bit(&num_cntrs_free_map,
>> +                    num_cntrs_free_map_len);
>> +
>> +    if (ctr_id >= num_cntrs_free_map_len)
>> +        return -ENOSPC;
>> +
>> +    __clear_bit(ctr_id, &num_cntrs_free_map);
>> +
>> +    return ctr_id;
>> +}
>> +
>>   /**
>>    * rdtgroup_mode_by_closid - Return mode of resource group with closid
>>    * @closid: closid if the resource group
>> @@ -1830,6 +1843,94 @@ static ssize_t 
>> mbm_local_bytes_config_write(struct kernfs_open_file *of,
>>       return ret ?: nbytes;
>>   }
>> +static void rdtgroup_abmc_cfg(void *info)
>> +{
>> +    u64 *msrval = info;
>> +
>> +    wrmsrl(MSR_IA32_L3_QOS_ABMC_CFG, *msrval);
>> +}
>> +
> 
> Please add comments to these functions to summarize what
> they do.

Sure.

> 
>> +int resctrl_arch_assign(struct rdt_domain *d, u32 evtid, u32 rmid,
>> +            u32 ctr_id, u32 closid, bool enable)
>> +{
>> +    struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
>> +    union l3_qos_abmc_cfg abmc_cfg = { 0 };
>> +    struct arch_mbm_state *arch_mbm;
>> +
>> +    abmc_cfg.split.cfg_en = 1;
>> +    abmc_cfg.split.ctr_en = enable ? 1 : 0;
>> +    abmc_cfg.split.ctr_id = ctr_id;
>> +    abmc_cfg.split.bw_src = rmid;
>> +
>> +    /*
>> +     * Read the event configuration from the domain and pass it as
>> +     * bw_type.
>> +     */
>> +    if (evtid == QOS_L3_MBM_TOTAL_EVENT_ID) {
>> +        abmc_cfg.split.bw_type = hw_dom->mbm_total_cfg;
>> +        arch_mbm = &hw_dom->arch_mbm_total[rmid];
>> +    } else {
>> +        abmc_cfg.split.bw_type = hw_dom->mbm_local_cfg;
>> +        arch_mbm = &hw_dom->arch_mbm_local[rmid];
>> +    }
>> +
>> +    smp_call_function_any(&d->cpu_mask, rdtgroup_abmc_cfg, &abmc_cfg, 
>> 1);
>> +
>> +    /* Reset the internal counters */
> 
> "internal counters"? This needs a definition ... but since this is not
> a new data structure the comment can be more specific about what is done
> and why.

How about?
/* Reset internal mbm event counters. */

> 
>> +    if (arch_mbm)
>> +        memset(arch_mbm, 0, sizeof(struct arch_mbm_state));
>> +
>> +    return 0;
> 
> If this function always succeeds then it can just be void?

Sure. We can do that.

> 
>> +}
>> +
>> +int resctrl_grp_assign(struct rdtgroup *rdtgrp, u32 evtid)
> 
> Please use consistent naming. Note how the filename is "rdtgroup.c" and 
> this
> function operates on "struct rdtgroup" and if you take a closer look at
> the functions in this file and the header where you add this function you
> will notice a distinct pattern of "rdtgroup_" used as prefix. There really
> is no reason to start a new namespace for this.

Sure.

> 
>> +{
>> +    struct rdt_resource *r = 
>> &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>> +    int ctr_id = 0, index;
>> +    struct rdt_domain *d;
>> +    u32 mon_state;
>> +
>> +    index = mon_event_config_index_get(evtid);
>> +    if (index == INVALID_CONFIG_INDEX) {
>> +        rdt_last_cmd_puts("Invalid event id\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    if (evtid == QOS_L3_MBM_TOTAL_EVENT_ID) {
>> +        mon_state = ASSIGN_TOTAL;
>> +    } else if (evtid == QOS_L3_MBM_LOCAL_EVENT_ID) {
>> +        mon_state = ASSIGN_LOCAL;
>> +    } else {
>> +        rdt_last_cmd_puts("Invalid event id\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    /* Nothing to do if event has been assigned already */
>> +    if (rdtgrp->mon.mon_state & mon_state) {
> 
> Why is this mon_state needed? Is it not redundant when considering that
> struct mongroup has an array of counter IDs that can already be used
> to see if a counter is assigned or not?
> What if there is a new:
> #define MON_CNTR_UNSET U32_MAX
> 
> When cntr_id[index] == MON_CNTR_UNSET then it is not assigned.

Yes. That can be done. That case mon_state is not required. We just need 
the index. Also, we need to initialize the ctrl_id when the group is 
created. Hope that should work.

> 
>> +        rdt_last_cmd_puts("ABMC counter is assigned already\n");
>> +        return 0;
>> +    }
>> +
>> +    /*
>> +     * Allocate a new counter and update domains
>> +     */
>> +    ctr_id = assign_cntrs_alloc();
>> +    if (ctr_id < 0) {
>> +        rdt_last_cmd_puts("Out of ABMC counters\n");
>> +        return -ENOSPC;
>> +    }
>> +
>> +    rdtgrp->mon.ctr_id[index] = ctr_id;
>> +
>> +    list_for_each_entry(d, &r->domains, list)
>> +        resctrl_arch_assign(d, evtid, rdtgrp->mon.rmid, ctr_id,
>> +                    rdtgrp->closid, 1);
>> +
>> +    rdtgrp->mon.mon_state |= mon_state;
>> +
>> +    return 0;
>> +}
>> +
>>   /* rdtgroup information files for one cache resource. */
>>   static struct rftype res_common_files[] = {
>>       {
> 
> Reinette
> 

-- 
- Babu Moger

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