linux-kernel - Re: RE: [PATCH v8 19/25] x86/resctrl: Auto assign/unassign counters when mbm_cntr

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Message-ID: <43654ae1-c894-409b-bcb8-065940644906@amd.com>
Date: Mon, 14 Oct 2024 10:43:00 -0500
From: "Moger, Babu" <babu.moger@....com>
To: "Luck, Tony" <tony.luck@...el.com>
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Subject: Re: RE: [PATCH v8 19/25] x86/resctrl: Auto assign/unassign counters
 when mbm_cntr_assign is enabled

Hi Tony,

On 10/11/24 16:33, Luck, Tony wrote:
>>>> +static int rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp)
>>>> +{
>>>> +  struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>>>> +  int ret = 0;
>>>> +
>>>> +  if (!resctrl_arch_mbm_cntr_assign_enabled(r))
>>>> +          return 0;
>>>> +
>>>> +  if (is_mbm_total_enabled())
>>>> +          ret = rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_TOTAL_EVENT_ID);
> 
> Consider that this call fails. "ret" indicates failure to allocate.

Look at this call

      if (is_mbm_total_enabled())
                ret = rdtgroup_assign_cntr_event(r, rdtgrp, NULL,
QOS_L3_MBM_TOTAL_EVENT_ID);


If this call fails, it will return immediately.

Lets say ret = 1; (1 if for failure. 0 for success)

> 
>>>> +
>>>> +  if (!ret && is_mbm_local_enabled())
>>>> +          ret = rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_LOCAL_EVENT_ID);
> 
> Now this call succeeds. The failure of the previous call is forgotten as "ret" is
> overwritten with the success code.

It will not make this call if the first call fails because of this check.

        if (!ret && is_mbm_local_enabled())
                ret = rdtgroup_assign_cntr_event(r, rdtgrp, NULL,
QOS_L3_MBM_LOCAL_EVENT_ID);

        return ret;

Here if (!1) evaluates to false.

Did I miss something?


> 
>>>
>>> This overwrites the value from allocating the counter for total event.
>>
>> Total event and local events have two different indexes.
>> Can you please elaborate?
> 
> See comments above.  If you want a return code you need
> 
> 	int ret_local = 0, ret_total = 0;
> 
> 	if (is_mbm_total_enabled())
> 		ret_total = rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_TOTAL_EVENT_ID);
> 	if (!ret && is_mbm_local_enabled())
> 		ret_local = rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_LOCAL_EVENT_ID);
> 
> 
> 	return some_function of ret_local and ret_total;
> 
> Not sure if you want to say success only if both of these calls succeeded. Or maybe if either worked?
> 
> But it all seems complicated since callers don't have to take any different action depending on whether allocation of a counter succeeds or fails.
> 
> -Tony
> 
> 
> 	

-- 
Thanks
Babu Moger