linux-kernel - Re: [PATCH v1 04/20] x86/resctrl: Add domain offline callback for resctrl work

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Date:   Wed, 11 Aug 2021 17:10:39 +0100
From:   Jamie Iles <jamie@...iainc.com>
To:     James Morse <james.morse@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        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,
        Jamie Iles <jamie@...iainc.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        lcherian@...vell.com, bobo.shaobowang@...wei.com
Subject: Re: [PATCH v1 04/20] x86/resctrl: Add domain offline callback for
 resctrl work

Hi James,

On Thu, Jul 29, 2021 at 10:35:54PM +0000, James Morse wrote:
> Because domains are exposed to user-space via resctrl, the filesystem
> must update its state when cpu hotplug callbacks are triggered.
> 
> Some of this work is common to any architecture that would support
> resctrl, but the work is tied up with the architecture code to
> free the memory.
> 
> Move the monitor subdir removal and the cancelling of the mbm/limbo
> works into a new resctrl_offline_domain() call.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     | 24 +---------------
>  arch/x86/kernel/cpu/resctrl/internal.h |  2 --
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 39 +++++++++++++++++++++++---
>  include/linux/resctrl.h                |  1 +
>  4 files changed, 37 insertions(+), 29 deletions(-)
...
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index e1af1d81b924..cf0db0b7a5d0 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
...
> @@ -3229,6 +3227,39 @@ static int __init rdtgroup_setup_root(void)
>  	return ret;
>  }
>  
> +void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
> +{
> +	lockdep_assert_held(&rdtgroup_mutex); // the arch code took this for us
> +
> +	if (!r->mon_capable)
> +		return;
> +
> +	/*
> +	 * If resctrl is mounted, remove all the
> +	 * per domain monitor data directories.
> +	 */
> +	if (static_branch_unlikely(&rdt_mon_enable_key))
> +		rmdir_mondata_subdir_allrdtgrp(r, d->id);
> +
> +	if (r->mon_capable && is_mbm_enabled())
> +		cancel_delayed_work(&d->mbm_over);

There's a redundant r->mon_capable check here.

> +	if (is_llc_occupancy_enabled() && has_busy_rmid(r, d)) {
> +		/*
> +		 * When a package is going down, forcefully
> +		 * decrement rmid->ebusy. There is no way to know
> +		 * that the L3 was flushed and hence may lead to
> +		 * incorrect counts in rare scenarios, but leaving
> +		 * the RMID as busy creates RMID leaks if the
> +		 * package never comes back.
> +		 */
> +		__check_limbo(d, true);
> +		cancel_delayed_work(&d->cqm_limbo);
> +	}
> +	bitmap_free(d->rmid_busy_llc);
> +	kfree(d->mbm_total);
> +	kfree(d->mbm_local);
> +}

Thanks,

Jamie