linux-kernel - Re: [PATCH] x86/resctrl: mba_MBps: Fall back to total b/w if local b/w unavailable

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Date:   Wed, 25 Oct 2023 18:41:49 -0500
From:   "Moger, Babu" <bmoger@....com>
To:     Tony Luck <tony.luck@...el.com>, "Moger, Babu" <babu.moger@....com>
Cc:     Peter Newman <peternewman@...gle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, x86@...nel.org,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH] x86/resctrl: mba_MBps: Fall back to total b/w if local
 b/w unavailable

Hi Tony,

On 10/25/2023 3:52 PM, Tony Luck wrote:
> On Wed, Oct 25, 2023 at 03:42:14PM -0500, Moger, Babu wrote:
>> I meant, I was thinking bit different.
>>
>>> You need these changes in only two functions, mbm_bw_count and
>>> update_mba_bw. You decide which event you want to use based on availability,
>>>
>>> Something like this. I updated mbm_bw_count.
>>>
>>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>>> index 0ad23475fe16..302993e4fbc3 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>>> @@ -436,8 +436,16 @@ static int __mon_event_count(u32 rmid, struct
>>> rmid_read *rr)
>>>    */
>>>   static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
>>>   {
>>> -       struct mbm_state *m = &rr->d->mbm_local[rmid];
>>>          u64 cur_bw, bytes, cur_bytes;
>>> +       struct mbm_state *m;
>>> +       int evtid;
>>> +
>>> +       if (is_mbm_local_enabled())
>>> +               evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
>>> +       else
>>> +               evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
>>> +
>>> +       m = get_mbm_state(rr->d, rmid, evtid);
> Ok. Yes. That seems simpler.
>
> Maybe I should just set a global "mbm_evtid" at mount

Lets not make it global yet. This is only affecting couple of functions 
when mba_MPps is enabled.

> time. No need to check every time to see if is_mbm_local_enabled()
> somehow changed and local b/w measurements were suddenly
> available!

What changed suddenly? Can you please elaborate.

Thanks

Babu