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References: <20240312075349.977-1-rex.nie@jaguarmicro.com> <fed6affb-c7f4-4992-8646-8f5a52c33966@intel.com>
In-Reply-To: <fed6affb-c7f4-4992-8646-8f5a52c33966@intel.com>
From: Peter Newman <peternewman@google.com>
Date: Thu, 14 Mar 2024 17:04:44 -0700
Message-ID: <CALPaoChnAt9+2=iVzpownX-bN+mb3Ujn_C=_QS2qsAph=LPSiA@mail.gmail.com>
Subject: Re: 32bit resctrl? (was Re: [PATCH v2] fs/resctrl: fix domid loss
 precision issue)
To: Rex Nie <rex.nie@jaguarmicro.com>
Cc: james.morse@arm.com, "x86@kernel.org" <x86@kernel.org>, "Luck, Tony" <tony.luck@intel.com>, 
	Babu Moger <babu.moger@amd.com>, Borislav Petkov <bp@alien8.de>, fenghua.yu@intel.com, 
	ilpo.jarvinen@linux.intel.com, linux-kernel@vger.kernel.org, 
	Reinette Chatre <reinette.chatre@intel.com>
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Hi Rex,

On Thu, Mar 14, 2024 at 8:25=E2=80=AFAM Reinette Chatre
<reinette.chatre@intel.com> wrote:
>
> +x86 maintainers, Tony, Babu, Peter
>
> Hi Everybody,
>
> On 3/12/2024 12:53 AM, Rex Nie wrote:
> > Below statement from mkdir_mondata_subdir function will loss precision,
> > because it assigns int to 14 bits bitfield.
> >       priv.u.domid =3D d->id;
> >
> > On some platforms(e.g.,x86), the max cache_id is the amount of L3 cache=
s,
> > so it is not in the range of 0x3fff. But some platforms use higher
> > cache_id, e.g., arm uses cache_id as locator for cache MSC. This will
> > cause below issue if cache_id > 0x3fff likes:
> > /sys/fs/resctrl/mon_groups/p1/mon_data/mon_L3_1048564 # cat llc_occupan=
cy

This domain ID seems unreadable in decimal and I'm wondering whether
it's the best value to use to identify the domain. Does this system
have over 1 million L3 domains?

Thanks!
-Peter