linux-kernel - Re: [PATCH] x86/intel_rdt: reinitialize cbm for new group allocation

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Date:   Mon, 9 Jan 2017 13:56:00 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Shaohua Li <shli@...com>
Cc:     linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/intel_rdt: reinitialize cbm for new group allocation

On Fri, Jan 06, 2017 at 04:05:19PM -0800, Shaohua Li wrote:
> rdtgroup_rmdir deletes a group and frees the closid, but doesn't
> reiniaialize domain's cbm to default for the closid. Next time the
> closid is allocated again, 'schemata' will show old cbm. We can do the
> reinitialization at free/alloc closid, but sounds doing it at alloc is
> more nartual.
> 
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Shaohua Li <shli@...com>
> ---
>  arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> index 8af04af..7e81527 100644
> --- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> +++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> @@ -78,12 +78,21 @@ static void closid_init(void)
>  int closid_alloc(void)
>  {
>  	int closid = ffs(closid_free_map);
> +	struct rdt_resource *r;
> +	struct rdt_domain *dom;
>  
>  	if (closid == 0)
>  		return -ENOSPC;
>  	closid--;
>  	closid_free_map &= ~(1 << closid);
>  
> +	for_each_enabled_rdt_resource(r) {
> +		if (closid >= r->num_closid)
> +			continue;
> +		list_for_each_entry(dom, &r->domains, list)
> +			dom->cbm[closid] = r->max_cbm;
> +	}
> +

This only changes the date stored in kernel software. But The cbm MSR
registers are not updated by the max_cbm. You need to call rdt_cbm_update
to update registers.

>  	return closid;
>  }
>  
> -- 
> 2.9.3
> 

I actually had a patch to fix this before but didn't send it out. I
thought this won't impact any functionality other than user may see some
unexpected schemata values, but user will always change schemata anyway
following mkdir.

But since you come here now,  I would think reseting the CBM in
closid_free() is better. The reason is user can see "right" max_cbm
even through rdmsr after rmdir, ie no gap for cbm values between rmdir and
the next mkdir.

Thanks.

-Fenghua