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Wed, 13 May 2020 20:04:00 +0000 Subject: RE: [PATCH v2 09/10] x86/resctrl: Add arch_has_sparse_bitmaps to explain AMD/Intel CAT difference To: Reinette Chatre , James Morse , "x86@kernel.org" , "linux-kernel@vger.kernel.org" Cc: Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin References: <20200430170400.21501-1-james.morse@arm.com> <20200430170400.21501-10-james.morse@arm.com> <8383ddd9-5849-d948-c391-aeb0cc927423@intel.com> From: Babu Moger Message-ID: <980a693a-b823-96e1-9b4f-d7bbf4f09714@amd.com> Date: Wed, 13 May 2020 15:03:57 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: <8383ddd9-5849-d948-c391-aeb0cc927423@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: DM5PR17CA0059.namprd17.prod.outlook.com (2603:10b6:3:13f::21) To SN1PR12MB2560.namprd12.prod.outlook.com (2603:10b6:802:26::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.236.30.87] (165.204.77.1) by DM5PR17CA0059.namprd17.prod.outlook.com (2603:10b6:3:13f::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.20 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: HxnJgKIXlzV1RTo8vCub89zMaXTKGZ7ckMu74rlULSgfBT1OZmIthee5u8lxwDP1AGNfEUQspJ97ax6A8HiE28tmyNEGszvp7sAPkYIJVHFncEuoikSUfXm93d2/Ob76yvORX0GQieVKS5h88mITP7ilgUuH0YLOb3pj4I3zdXkt1OFkfdbsNBrFUyHX89H/+zHnZZQcTaDpjIRpqnCQGlc8zYXZqUvqVaEvPBe+Zk0FXv0bNn46fFE9/NChPgmgmSL4THMobr00UWFQZHv52F3tf+vm/t5JzoFWN/SUFFkfS+BIVM+PNuZ0WVWTpjZtqVjtZeXXbNPjTtYkDbL60k1naEdEWUzokW467bPj0/iKNA9+W8Rh8/oCZ2g3ZtoYKZAxgOQaz27GnoBmAVTJHsOw6wZwiw7K9net4sJ8U+uQhsVYIAxD3i+XQzdYUE17HliYu2DJOTgYNuoYUwCtryTiHoYu1uKX5UdqQAIjCqM= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 55cac04e-c07a-421f-ec06-08d7f778c6b6 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 May 2020 20:03:59.9796 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 7l6fH7ifX4K+cCUOHFxjQ6cA4HxIEo/kv449KMA/2+hRm4RV3tSk1PEtoxieKHxX X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN1PR12MB2352 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Reinette Chatre > Sent: Monday, May 11, 2020 1:15 PM > To: James Morse ; x86@kernel.org; linux- > kernel@vger.kernel.org > Cc: Fenghua Yu ; Thomas Gleixner > ; Ingo Molnar ; Borislav Petkov > ; H Peter Anvin ; Moger, Babu > > Subject: Re: [PATCH v2 09/10] x86/resctrl: Add arch_has_sparse_bitmaps to > explain AMD/Intel CAT difference > > Hi James, > > On 4/30/2020 10:03 AM, James Morse wrote: > > Intel expects the cache bitmap provided by user-space to have on a > > single span of 1s, whereas AMD can support bitmaps like 0xf00f. > > Arm's MPAM support also allows sparse bitmaps. > > > > To move resctrl out to /fs/ we need to explain platform differences > > like this. Add a resource property arch_has_sparse_bitmaps. Test this > > around the 'non-consecutive' test in cbm_validate(). > > > > Merging the validate calls causes AMD top gain the min_cbm_bits test > > needed for Haswell, but as it always sets this value to 1, it will > > never match. > > > > CC: Babu Moger > > Signed-off-by: James Morse > > Reviewed-by: Reinette Chatre > > The Intel bits do indeed look good to me but we should check the AMD > portion ... I peeked at the AMD spec [1] and found "If an L3_MASK_n > register is programmed with all 0’s, that COS will be prevented from > allocating any lines in the L3 cache" ... so AMD does allow bitmasks of > all 0's (Intel does not). > > Does MPAM also allow all 0's? Perhaps "arch_has_sparse_bitmaps" can be > used to indicate that also? That is right. AMD allows L3 mask be all 0s. I will be great if this property can be indicated it here. Thanks