linux-kernel - Re: [PATCH v8 02/21] x86/resctrl: Remove the limit on the number of CLOSID

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Message-ID: <9f7c6c14-ba6d-48ef-baea-7c313813d513@intel.com>
Date: Tue, 15 Apr 2025 14:06:34 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: 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>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
	"Dave Martin" <dave.martin@....com>, Koba Ko <kobak@...dia.com>, Shanker
 Donthineni <sdonthineni@...dia.com>, <fenghuay@...dia.com>, Shaopeng Tan
	<tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v8 02/21] x86/resctrl: Remove the limit on the number of
 CLOSID

Hi James,

On 4/11/25 9:42 AM, James Morse wrote:
> From: Amit Singh Tomar <amitsinght@...vell.com>
> 
> Resctrl allocates and finds free CLOSID values using the bits of a u32.
> This restricts the number of control groups that can be created by
> user-space.
> 
> MPAM has an architectural limit of 2^16 CLOSID values, Intel x86 could
> be extended beyond 32 values. There is at least one MPAM platform which
> supports more than 32 CLOSID values.
> 
> Replace the fixed size bitmap with calls to the bitmap API to allocate
> an array of a sufficient size.
> 
> ffs() returns '1' for bit 0, hence the existing code subtracts 1 from
> the index to get the CLOSID value. find_first_bit() returns the bit
> number which does not need adjusting.
> 
> Signed-off-by: Amit Singh Tomar <amitsinght@...vell.com>
> [ morse: fixed the off-by-one in the allocator and the wrong
>  not-found value. Removed the limit. Rephrase the commit message. ]
> Signed-off-by: James Morse <james.morse@....com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Tested-by: Amit Singh Tomar <amitsinght@...vell.com> # arm64
> Tested-by: Shanker Donthineni <sdonthineni@...dia.com> # arm64
> Tested-by: Babu Moger <babu.moger@....com>
> Reviewed-by: Fenghua Yu <fenghuay@...dia.com>
> ---

Thank you.

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette