linux-kernel - Re: [PATCH 06/18] x86/resctrl: Allow the allocator to check if a CLOSID can allocate clean RMID

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Date:   Tue, 8 Nov 2022 23:57:57 +0800
From:   Shawn Wang <shawnwang@...ux.alibaba.com>
To:     James Morse <james.morse@....com>, x86@...nel.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,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, xingxin.hx@...nanolis.org,
        baolin.wang@...ux.alibaba.com, peternewman@...gle.com
Subject: Re: [PATCH 06/18] x86/resctrl: Allow the allocator to check if a
 CLOSID can allocate clean RMID

Hi James,

On 10/21/2022 9:11 PM, James Morse wrote:
> MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
> used for different control groups.
> 
> This means once a CLOSID is allocated, all its monitoring ids may still be
> dirty, and held in limbo.
> 
> Add a helper to allow the CLOSID allocator to check if a CLOSID has dirty
> RMID values. This behaviour is enabled by a kconfig option selected by
> the architecture, which avoids a pointless search for x86.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
>   arch/x86/kernel/cpu/resctrl/internal.h |  1 +
>   arch/x86/kernel/cpu/resctrl/monitor.c  | 31 ++++++++++++++++++++++++++
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 18 +++++++++------
>   3 files changed, 43 insertions(+), 7 deletions(-)

> +/**
> + * resctrl_closid_is_dirty - Determine if clean RMID can be allocate for this
> + *                           CLOSID.
> + * @closid: The CLOSID that is being queried.
> + *
> + * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocate CLOSID
> + * may not be able to allocate clean RMID. To avoid this the allocator will
> + * only return clean CLOSID.
> + */
> +bool resctrl_closid_is_dirty(u32 closid)
> +{
> +	struct rmid_entry *entry;
> +	int i;
> +
> +	lockdep_assert_held(&rdtgroup_mutex);
> +
> +	if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
> +		return false;

Since dirty closid occurs when the kconfig option for MPAM is enabled, it seems
that the condition of the if statement here should take the opposite value:
	if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))

> +
> +	for (i = 0; i < resctrl_arch_system_num_rmid_idx(); i++) {
> +		entry = &rmid_ptrs[i];
> +		if (entry->closid != closid)
> +			continue;
> +
> +		if (entry->busy)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +

Shawn