linux-kernel - Re: [PATCH v8 10/13] x86/resctrl: Add sysfs interface to write mbm_total_bytes

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Message-ID: <5ce5bdd7-c2ee-fa7c-a01c-174ee3ee24d8@intel.com>
Date:   Tue, 22 Nov 2022 15:43:08 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     <babu.moger@....com>, Peter Newman <peternewman@...gle.com>
CC:     <akpm@...ux-foundation.org>, <bagasdotme@...il.com>,
        <bp@...en8.de>, <chang.seok.bae@...el.com>, <corbet@....net>,
        <damien.lemoal@...nsource.wdc.com>,
        <daniel.sneddon@...ux.intel.com>, <dave.hansen@...ux.intel.com>,
        <eranian@...gle.com>, <fenghua.yu@...el.com>, <hpa@...or.com>,
        <james.morse@....com>, <jmattson@...gle.com>,
        <jpoimboe@...nel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <paulmck@...nel.org>, <pawan.kumar.gupta@...ux.intel.com>,
        <pbonzini@...hat.com>, <peterz@...radead.org>,
        <quic_neeraju@...cinc.com>, <rdunlap@...radead.org>,
        <sandipan.das@....com>, <songmuchun@...edance.com>,
        <tglx@...utronix.de>, <tony.luck@...el.com>, <x86@...nel.org>
Subject: Re: [PATCH v8 10/13] x86/resctrl: Add sysfs interface to write
 mbm_total_bytes_config

Hi Babu,

On 11/7/2022 11:00 AM, Moger, Babu wrote:
> 
> On 11/7/22 04:21, Peter Newman wrote:
>> Hi Babu,
>>
>> On Fri, Nov 04, 2022 at 03:01:09PM -0500, Babu Moger wrote:
>>> +	/*
>>> +	 * When an Event Configuration is changed, the bandwidth counters
>>> +	 * for all RMIDs and Events will be cleared by the hardware. The
>>> +	 * hardware also sets MSR_IA32_QM_CTR.Unavailable (bit 62) for
>>> +	 * every RMID on the next read to any event for every RMID.
>>> +	 * Subsequent reads will have MSR_IA32_QM_CTR.Unavailable (bit 62)
>>> +	 * cleared while it is tracked by the hardware. Clear the
>>> +	 * mbm_local and mbm_total counts for all the RMIDs.
>>> +	 */
>>> +	memset(d->mbm_local, 0, sizeof(struct mbm_state) * r->num_rmid);
>>> +	memset(d->mbm_total, 0, sizeof(struct mbm_state) * r->num_rmid);
>> Looking around, I can't find a reader for mbm_total anymore. It looks
>> like the last place it was used went away in James's recent change:
>>
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20220902154829.30399-19-james.morse%40arm.com&amp;data=05%7C01%7Cbabu.moger%40amd.com%7C84a9d0f934894a3031a608dac0a9db33%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638034133003350939%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=i3isjCzxnBp4b2VblC7ZpH3hShUEe7unKiKfngG1kzE%3D&amp;reserved=0
>>
>> Are we supposed to be clearing arch_mbm_total now?
>>
> Patch got garbled in previous response.
> 
> Here is it now.
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 6b222f8e58ae..28d9d99a639e 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1517,7 +1517,7 @@ static int mbm_config_write(struct rdt_resource *r,
> struct rdt_domain *d,
>                             u32 evtid, u32 val)
>  {
>         struct mon_config_info mon_info = {0};
> -       int ret = 0;
> +       int ret = 0, i;
>  
>         rdt_last_cmd_clear();
>  
> @@ -1557,8 +1557,10 @@ static int mbm_config_write(struct rdt_resource *r,
> struct rdt_domain *d,
>          * cleared while it is tracked by the hardware. Clear the
>          * mbm_local and mbm_total counts for all the RMIDs.
>          */
> -       memset(d->mbm_local, 0, sizeof(struct mbm_state) * r->num_rmid);
> -       memset(d->mbm_total, 0, sizeof(struct mbm_state) * r->num_rmid);
> +       for (i = 0; i < r->num_rmid; i++) {
> +               resctrl_arch_reset_rmid(r, d, i, QOS_L3_MBM_TOTAL_EVENT_ID);
> +               resctrl_arch_reset_rmid(r, d, i, QOS_L3_MBM_LOCAL_EVENT_ID);
> +       }
>  
>  write_exit:
>         return ret;

Resetting each member of an array individually seems unnecessary when the
array could just be reset as a unit. How about instead a new
resctrl_arch_reset_rmid_all() that can do so?

Reinette