linux-kernel - Re: [PATCH v6 05/24] x86/resctrl: Track the closid with the rmid

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Date:   Tue, 3 Oct 2023 14:11:39 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Fenghua Yu <fenghua.yu@...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>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        <carl@...amperecomputing.com>, <lcherian@...vell.com>,
        <bobo.shaobowang@...wei.com>, <tan.shaopeng@...itsu.com>,
        <xingxin.hx@...nanolis.org>, <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, <peternewman@...gle.com>,
        <dfustini@...libre.com>, <amitsinght@...vell.com>
Subject: Re: [PATCH v6 05/24] x86/resctrl: Track the closid with the rmid

Hi James,

On 9/14/2023 10:21 AM, James Morse wrote:

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index cfb3f632a4b2..42b9a694fe2f 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -24,7 +24,21 @@
>  
>  #include "internal.h"
>  
> +/**
> + * struct rmid_entry - dirty tracking for all RMID.
> + * @closid:	The CLOSID for this entry.
> + * @rmid:	The RMID for this entry.
> + * @busy:	The number of domains with cached data using this RMID.
> + * @list:	Member of the rmid_free_lru list when busy == 0.
> + *
> + * Some architectures's resctrl_arch_rmid_read() needs the CLOSID value
> + * in order to access the correct monitor. @closid provides the value to
> + * list walkers like __check_limbo(). On x86 this is ignored.

I do not think this is correct. At this point in the series
__check_limbo() uses @rmid as index, at end of series it uses the
(@closid, @rmid) index. Never does the list walker use @closid.

Perhaps something like below that matches your later similar comments:

	Depending on the architecture the correct monitor is accessed
	using both @closid and @rmid, or @rmid only.


...

  
> @@ -685,11 +706,11 @@ void mbm_handle_overflow(struct work_struct *work)
>  	d = container_of(work, struct rdt_domain, mbm_over.work);
>  
>  	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
> -		mbm_update(r, d, prgrp->mon.rmid);
> +		mbm_update(r, d, prgrp->closid, prgrp->mon.rmid);
>  
>  		head = &prgrp->mon.crdtgrp_list;
>  		list_for_each_entry(crgrp, head, mon.crdtgrp_list)
> -			mbm_update(r, d, crgrp->mon.rmid);
> +			mbm_update(r, d, crgrp->closid, crgrp->mon.rmid);
>  
>  		if (is_mba_sc(NULL))
>  			update_mba_bw(prgrp, d);
> @@ -732,10 +753,11 @@ static int dom_data_init(struct rdt_resource *r)
>  	}
>  
>  	/*
> -	 * RMID 0 is special and is always allocated. It's used for all
> -	 * tasks that are not monitored.
> +	 * RESCTRL_RESERVED_CLOSID and RESCTRL_RESERVED_RMID are special and
> +	 * are always allocated. These are used for rdtgroup_default control
> +	 * group, which will be setup later. See rdtgroup_setup_root().
>  	 */

This comment will not be accurate after Babu's changes are merged (the function will
be rdtgroup_setup_default()). To avoid that conflict you could perhaps change
last two sentences to something like below that will be accurate no matter the
order of merging between your and Babu's work:

	These are used for rdtgroup_default control group, which will be
	setup later in rdtgroup_init().

> -	entry = __rmid_entry(0);
> +	entry = __rmid_entry(RESCTRL_RESERVED_CLOSID, RESCTRL_RESERVED_RMID);
>  	list_del(&entry->list);
>  
>  	return 0;


My feedback only relates to the comments. The rest of the patch looks good to
me. I could give a review tag with expectation that comments be addressed in next
version but since some review feedback fell through the cracks in this version I
feel that I need to confirm first before providing review tag.

Reinette