linux-kernel - RE: [PATCH v2 12/23] x86/resctrl: Abstract and use supports_mba

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Date:   Thu, 7 Oct 2021 06:13:28 +0000
From:   "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>
To:     'James Morse' <james.morse@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.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" 
        <shameerali.kolothum.thodi@...wei.com>,
        Jamie Iles <jamie@...iainc.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        "lcherian@...vell.com" <lcherian@...vell.com>,
        "bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>
Subject: RE: [PATCH v2 12/23] x86/resctrl: Abstract and use
 supports_mba_mbps()

Hi James,

> To determine whether the mba_MBps option to resctrl should be supported,
> resctrl tests the boot cpus' x86_vendor.
> 
> This isn't portable, and needs abstracting behind a helper so this check can be
> part of the filesystem code that moves to /fs/.
> 
> Re-use the tests set_mba_sc() does to determine if the mba_sc is supported
> on this system. An 'alloc_capable' test is added so that support for the controls
> isn't implied by the 'delay_linear' property, which is always true for MPAM.
> 
> Signed-off-by: James Morse <james.morse@....com>

Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>

> ---
> Changes since v1:
>  * Capitalisation
>  * Added MPAM example in commit message
>  * Fixed supports_mba_mbps() logic error in rdt_parse_param()
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 069c209be1d5..1207271cce23 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1948,17 +1948,26 @@ static void mba_sc_destroy(struct rdt_resource
> *r)  }
> 
>  /*
> - * Enable or disable the MBA software controller
> - * which helps user specify bandwidth in MBps.
>   * MBA software controller is supported only if
>   * MBM is supported and MBA is in linear scale.
>   */
> +static bool supports_mba_mbps(void)
> +{
> +	struct rdt_resource *r =
> +&rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
> +
> +	return (is_mbm_enabled() &&
> +		r->alloc_capable && is_mba_linear()); }
> +
> +/*
> + * Enable or disable the MBA software controller
> + * which helps user specify bandwidth in MBps.
> + */
>  static int set_mba_sc(bool mba_sc)
>  {
>  	struct rdt_resource *r =
> &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
> 
> -	if (!is_mbm_enabled() || !is_mba_linear() ||
> -	    mba_sc == is_mba_sc(r))
> +	if (!supports_mba_mbps() || mba_sc == is_mba_sc(r))
>  		return -EINVAL;
> 
>  	r->membw.mba_sc = mba_sc;
> @@ -2317,7 +2326,7 @@ static int rdt_parse_param(struct fs_context *fc,
> struct fs_parameter *param)
>  		ctx->enable_cdpl2 = true;
>  		return 0;
>  	case Opt_mba_mbps:
> -		if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
> +		if (!supports_mba_mbps())
>  			return -EINVAL;
>  		ctx->enable_mba_mbps = true;
>  		return 0;
> --
> 2.30.2

Regards,
Shaopeng Tan