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 15:39:30 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Tony Luck <tony.luck@...el.com>,
        Peter Newman <peternewman@...gle.com>
Cc:     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 10/25/23 14:38, Tony Luck wrote:
> On Wed, Oct 25, 2023 at 02:46:53PM +0200, Peter Newman wrote:
>> Hi Tony,
>>
>> On Tue, Oct 24, 2023 at 8:16 PM Tony Luck <tony.luck@...el.com> wrote:
>>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>>> @@ -418,6 +418,14 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
>>>         return 0;
>>>  }
>>>
>>> +static struct mbm_state *get_mbm_data(struct rdt_domain *dom_mbm, int rmid)
>>> +{
>>> +       if (is_mbm_local_enabled())
>>> +               return &dom_mbm->mbm_local[rmid];
>>> +
>>> +       return &dom_mbm->mbm_total[rmid];
>>> +}
>>
>> That looks very similar to the get_mbm_state() function I added to
>> this same file recently:
>>
>> https://lore.kernel.org/all/20221220164132.443083-2-peternewman%40google.com
>>
>> I think the name you picked is misleadingly general. "local if
>> available, otherwise total" seems to be a choice specific to the mbps
>> controller. I think these functions should be reconciled a little
>> better.
>>
> 
> Peter (and Babu, who made the same point about get_mbm_state().
> 
> Do you want to see your function extended to do the "pick an MBM event?"
> 
> I could add a s/w defined "event" to the enum resctrl_event_id and
> extend get_mbm_state() like this:
> 
> 
> static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 rmid,
> 				       enum resctrl_event_id evtid)
> {
> 	switch (evtid) {
> 	case QOS_L3_MBM_TOTAL_EVENT_ID:
> 		return &d->mbm_total[rmid];
> 	case QOS_L3_MBM_LOCAL_EVENT_ID:
> 		return &d->mbm_local[rmid];
> +	case QOS_L3_MBM_LOCAL_OR_TOTAL_EVENT_ID:
> +		if (is_mbm_local_enabled())
> +			return &d->mbm_local[rmid];
> +		if (is_mbm_total_enabled())
> +			return &d->mbm_total[rmid];
> +		fallthrough;
> 	default:
> 		return NULL;
> 	}
> }
> 
> Is this the direction you are thinking of?

No. I was not 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);

        cur_bytes = rr->val;
        bytes = cur_bytes - m->prev_bw_bytes;


Will this work?

Thanks
Babu


> 
> Callers then look like:
> 
> static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
> {
> 	struct mbm_state *m = get_mbm_state(rr->d, rmid, QOS_L3_MBM_LOCAL_OR_TOTAL_EVENT_ID);
> 	u64 cur_bw, bytes, cur_bytes;
> 
> similar for the other three places where this is needed.
> 
> Any suggestions on how "QOS_L3_MBM_LOCAL_OR_TOTAL_EVENT_ID" could be
> abbreviated, or just have some different, but descriptive, name?
> 
> -Tony

-- 
Thanks
Babu Moger