linux-kernel - Re: [PATCH v2 4/4] x86/resctrl: Rename arch_has_sparse

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Message-ID: <27gd4em7og62jn4v364emkthna5a2f63nvlxigvyh4p74bcyzo@llgj56vewc73>
Date:   Fri, 29 Sep 2023 08:20:54 +0200
From:   Maciej Wieczór-Retman 
        <maciej.wieczor-retman@...el.com>
To:     Reinette Chatre <reinette.chatre@...el.com>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] x86/resctrl: Rename arch_has_sparse_bitmaps

On 2023-09-28 at 13:47:49 -0700, Reinette Chatre wrote:
>Hi Maciej
>
>Could you please move this patch to the beginning of this series?
>Having it in the end results in a lot of churn with significant
>changes to new code introduced in this series. All this can be avoided
>by providing a smaller patch at the beginning of the series.

Sure

>On 9/22/2023 1:48 AM, Maciej Wieczor-Retman wrote:
>> Both AMD and Intel documentations use capacity bitmasks terminology
>> rather than capacity bitmaps. Also bitmask term is much more widely
>> used inside x86 resctrl code.
>
>Since resctrl is intended to support many architectures and Arm coming
>soon (and they use bitmap) I do not think we should use the vendor's
>language as a motivation. For me there are three reasons supporting the
>rename:
>* arch_has_sparse_bitmaps is the *only* instance in resctrl that uses
>  the bitmap term for capacity bitmasks, all other parts of resctrl refers
>  to it as a bitmask
>* bitmask is the established term used in resctrl documentation
>  (Documentation/arch/x86/resctrl.rst)
>* bitmask is the term already exposed to user space via resctrl ("cbm_mask")
>
>Finally, why do the rename as part of this work? This can be motivated
>with something like:
>	A later patch exposes the value of arch_has_sparse_bitmaps to
>	user space via the existing term of a bitmask. Rename
>	arch_has_sparse_bitmaps to arch_has_sparse_bitmasks to ensure 
>	consistent terminology throughout resctrl.

Okay, I see your point. My only reason for mentioning x86 was that the
changes are done in arch/x86 directory. But I can see that there is no
need to mention it here really. I'll redo the patch message accordingly.

>> 
>> Unify the naming convention by renaming arch_has_sparse_bitmaps struct
>> member to arch_has_sparse_bitmasks.
>> 
>> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
>> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
>> ---
>
>...
>
>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>> index 8334eeacfec5..83c2cbf7136d 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -57,7 +57,7 @@ struct resctrl_staged_config {
>>   * @list:		all instances of this resource
>>   * @id:			unique id for this instance
>>   * @cpu_mask:		which CPUs share this resource
>> - * @rmid_busy_llc:	bitmap of which limbo RMIDs are above threshold
>> + * @rmid_busy_llc:	bitmask of which limbo RMIDs are above threshold
>>   * @mbm_total:		saved state for MBM total bandwidth
>>   * @mbm_local:		saved state for MBM local bandwidth
>>   * @mbm_over:		worker to periodically read MBM h/w counters
>
>Please drop this hunk. rmid_busy_llc is indeed a bitmap.

Okay, thanks for catching this.

-- 
Kind regards
Maciej Wieczór-Retman