linux-kernel - Re: [PATCH v5 04/24] x86/resctrl: Move rmid allocation out of mkdir_rdt

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Date:   Mon, 14 Aug 2023 17:50:41 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     James Morse <james.morse@....com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     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>,
        <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>
Subject: Re: [PATCH v5 04/24] x86/resctrl: Move rmid allocation out of
 mkdir_rdt_prepare()

Hi, James,

On 7/28/23 09:42, James Morse wrote:
> RMID are allocated for each monitor or control group directory, because
> each of these needs its own RMID. For control groups,
> rdtgroup_mkdir_ctrl_mon() later goes on to allocate the CLOSID.
> 
> MPAM's equivalent of RMID is not an independent number, so can't be
> allocated until the CLOSID is known. An RMID allocation for one CLOSID
> may fail, whereas another may succeed depending on how many monitor
> groups a control group has.
> 
> The RMID allocation needs to move to be after the CLOSID has been
> allocated.
> 
> Move the RMID allocation out of mkdir_rdt_prepare() to occur in its caller,
> after the mkdir_rdt_prepare() call. This allows the RMID allocator to
> know the CLOSID.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v2:
>   * Moved kernfs_activate() later to preserve atomicity of files being visible
> ---
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 35 +++++++++++++++++++-------
>   1 file changed, 26 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index e7178bbbd30f..7c5cfb373d03 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3189,6 +3189,12 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
>   	return 0;
>   }
>   
> +static void mkdir_rdt_prepare_rmid_free(struct rdtgroup *rgrp)
> +{
> +	if (rdt_mon_capable)
> +		free_rmid(rgrp->closid, rgrp->mon.rmid);
> +}
> +
>   static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>   			     const char *name, umode_t mode,
>   			     enum rdt_group_type rtype, struct rdtgroup **r)
> @@ -3254,12 +3260,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>   		goto out_destroy;
>   	}
>   
> -	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> -	if (ret)
> -		goto out_destroy;
> -
> -	kernfs_activate(kn);
> -
>   	/*
>   	 * The caller unlocks the parent_kn upon success.
>   	 */
> @@ -3278,7 +3278,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
>   static void mkdir_rdt_prepare_clean(struct rdtgroup *rgrp)
>   {
>   	kernfs_remove(rgrp->kn);
> -	free_rmid(rgrp->closid, rgrp->mon.rmid);
>   	rdtgroup_remove(rgrp);
>   }
>   
> @@ -3300,12 +3299,21 @@ static int rdtgroup_mkdir_mon(struct kernfs_node *parent_kn,
>   	prgrp = rdtgrp->mon.parent;
>   	rdtgrp->closid = prgrp->closid;
>   
> +	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> +	if (ret) {
> +		mkdir_rdt_prepare_clean(rdtgrp);
> +		goto out_unlock;
> +	}
> +
> +	kernfs_activate(rdtgrp->kn);
> +
>   	/*
>   	 * Add the rdtgrp to the list of rdtgrps the parent
>   	 * ctrl_mon group has to track.
>   	 */
>   	list_add_tail(&rdtgrp->mon.crdtgrp_list, &prgrp->mon.crdtgrp_list);
>   
> +out_unlock:
>   	rdtgroup_kn_unlock(parent_kn);
>   	return ret;
>   }
> @@ -3336,10 +3344,17 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
>   	ret = 0;
>   
>   	rdtgrp->closid = closid;
> -	ret = rdtgroup_init_alloc(rdtgrp);
> -	if (ret < 0)
> +
> +	ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> +	if (ret)
>   		goto out_id_free;

Is it better to change "out_id_free" to "out_closid_free"?
It's not confused to name it "out_id_free" because only closid is freed.
But this patch introduces new "rmid" free. So it's better to rename the 
label to "out_closid_free" and it matches the following "out_rmid_free" 
as well.

>   
> +	kernfs_activate(rdtgrp->kn);
> +
> +	ret = rdtgroup_init_alloc(rdtgrp);
> +	if (ret < 0)
> +		goto out_rmid_free;
> +
>   	list_add(&rdtgrp->rdtgroup_list, &rdt_all_groups);
>   
>   	if (rdt_mon_capable) {
> @@ -3358,6 +3373,8 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
>   
>   out_del_list:
>   	list_del(&rdtgrp->rdtgroup_list);
> +out_rmid_free:
> +	mkdir_rdt_prepare_rmid_free(rdtgrp);
>   out_id_free:

s/out_id_free/out_closid_free/?

>   	closid_free(closid);
>   out_common_fail:

Thanks.

-Fenghua