linux-kernel - Re: [PATCH v6 22/30] x86/resctrl: Read core telemetry events

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Message-ID: <fb180b2e-8677-4533-81e2-174d427f59c2@intel.com>
Date: Wed, 9 Jul 2025 15:13:38 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>
CC: Fenghua Yu <fenghuay@...dia.com>, Maciej Wieczor-Retman
	<maciej.wieczor-retman@...el.com>, Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>, "Drew
 Fustini" <dfustini@...libre.com>, Dave Martin <Dave.Martin@....com>, "Anil
 Keshavamurthy" <anil.s.keshavamurthy@...el.com>, Chen Yu
	<yu.c.chen@...el.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v6 22/30] x86/resctrl: Read core telemetry events

Hi Tony,

On 7/9/25 2:57 PM, Luck, Tony wrote:
> On Wed, Jul 09, 2025 at 08:48:47AM -0700, Reinette Chatre wrote:
>> Hi Tony,
>>
>> What does the "core" in the subject refer to?
> 
> The events are collected by each core. But since resctrl reports the
> aggregated per-package values this is confusing. I'll drop "core" from
> the Subject line.
> 
> [snip]
> 
>>> +/*
>>> + * Read counter for an event on a domain (summing all aggregators
>>> + * on the domain).
>>> + */
>>> +int intel_aet_read_event(int domid, int rmid, enum resctrl_event_id eventid,
>>> +			 void *arch_priv, u64 *val)
>>> +{
>>> +	struct pmt_event *pevt = arch_priv;
>>> +	struct mmio_info *mmi;
>>> +	struct event_group *e;
>>> +	u64 evtcount;
>>> +	void *pevt0;
>>
>> Should this be a struct pmt_event *?
> 
> I thought that too. But container_of() gets confused about types (I
> think because the evts[] element is a flex array.
> 
> With "struct pmt_event *pevt0;" the compiler complains:
> 
> arch/x86/kernel/cpu/resctrl/intel_aet.c: In function ‘intel_aet_read_event’:
> ./include/linux/build_bug.h:78:41: error: static assertion failed: "pointer type mismatch in container_of()"
>    78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
>       |                                         ^~~~~~~~~~~~~~
> ./include/linux/build_bug.h:77:34: note: in expansion of macro ‘__static_assert’
>    77 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
>       |                                  ^~~~~~~~~~~~~~~
> ./include/linux/container_of.h:20:9: note: in expansion of macro ‘static_assert’
>    20 |         static_assert(__same_type(*(ptr), ((type *)0)->member) ||       \
>       |         ^~~~~~~~~~~~~
> arch/x86/kernel/cpu/resctrl/intel_aet.c:311:13: note: in expansion of macro ‘container_of’
>   311 |         e = container_of(pevt0, struct event_group, evts);
>       |             ^~~~~~~~~~~~
> 
> Making it void * is the "get of of jail free" case in container_of()
> with the test " || __same_type(*(ptr), void)"
> 
> If there is a better way to do this, let me know.

Thanks for investigating. I did not consider this.

Reinette