linux-kernel - Re: [PATCH v4 17/39] x86/resctrl: Rewrite and move the for_each_*_rdt

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Message-ID: <5492c93e-b6c6-4443-afd3-b30c6267c2ab@arm.com>
Date: Mon, 30 Sep 2024 17:42:31 +0100
From: James Morse <james.morse@....com>
To: "Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>,
 "x86@...nel.org" <x86@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: Fenghua Yu <fenghua.yu@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
 Babu Moger <Babu.Moger@....com>,
 "shameerali.kolothum.thodi@...wei.com"
 <shameerali.kolothum.thodi@...wei.com>,
 D Scott Phillips OS <scott@...amperecomputing.com>,
 "carl@...amperecomputing.com" <carl@...amperecomputing.com>,
 "lcherian@...vell.com" <lcherian@...vell.com>,
 "bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
 "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
 Jamie Iles <quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
 "peternewman@...gle.com" <peternewman@...gle.com>,
 "dfustini@...libre.com" <dfustini@...libre.com>,
 "amitsinght@...vell.com" <amitsinght@...vell.com>,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v4 17/39] x86/resctrl: Rewrite and move the
 for_each_*_rdt_resource() walkers

Hi Shaopeng Tan,

On 15/08/2024 07:43, Shaopeng Tan (Fujitsu) wrote:
>> Subject: [PATCH v4 17/39] x86/resctrl: Rewrite and move the
>> for_each_*_rdt_resource() walkers
>>
>> The for_each_*_rdt_resource() helpers walk the architecture's array of
>> structures, using the resctrl visible part as an iterator. These became
>> over-complex when the structures were split into a filesystem and
>> architecture-specific struct. This approach avoided the need to touch every call
>> site, and was done before there was a helper to retrieve a resource by rid.
>>
>> Once the filesystem parts of resctrl are moved to /fs/, both the architecture's
>> resource array, and the definition of those structures is no longer accessible. To
>> support resctrl, each architecture would have to provide equally complex
>> macros.
>>
>> Rewrite the macro to make use of resctrl_arch_get_resource(), and move these
>> to the core header so existing x86 arch code continues to use them.

>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
>> b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 8e52e81a044b..84e0d019423d 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -472,14 +472,6 @@ extern struct rdt_hw_resource rdt_resources_all[];

>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h index
>> c8cd6dde91ed..04a410a5e739 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -26,6 +26,24 @@ int proc_resctrl_show(struct seq_file *m,
>>  /* max value for struct rdt_domain's mbps_val */
>>  #define MBA_MAX_MBPS   U32_MAX
>>
>> +/* Walk all possible resources, with variants for only controls or monitors. */
>> +#define for_each_rdt_resource(_r)
>> 	\
>> +	for ((_r) = resctrl_arch_get_resource(0);				\
>> +	     (_r)->rid < RDT_NUM_RESOURCES - 1;
>> 		\
>> +	     (_r) = resctrl_arch_get_resource((_r)->rid + 1))
>> +
>> +#define for_each_capable_rdt_resource(r)
>> \
>> +	for_each_rdt_resource((r))
>> \
>> +		if ((r)->alloc_capable || (r)->mon_capable)
>> +
>> +#define for_each_alloc_capable_rdt_resource(r)
>> \
>> +	for_each_rdt_resource((r))
>> \
>> +		if ((r)->alloc_capable)
>> +
>> +#define for_each_mon_capable_rdt_resource(r)
>> \
>> +	for_each_rdt_resource((r))
>> \
>> +		if ((r)->mon_capable)
>> +

> ERROR: Macros with complex values should be enclosed in parentheses

This is from checkpatch - I've ignored it because the 'r' values are in parenthesis...

I _think_ what it wants is this:               \|/
| #define for_each_mon_capable_rdt_resource(r)	(	\
|        for_each_rdt_resource((r))			\
|		if ((r)->mon_capable))			\

but then this macro wouldn't work in the way it is intended to be used because it breaks
the deliberately dangling if statement

Checkpatch also complains about the existing code.

I think this is just a pattern of code that is frowned on (including by me!). Previous
versions of this series rolled these out as a loop and condition at each call site, but
Reinette didn't think this was worth the churn as the existing helpers are well understood.


Thanks,

James