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Fri, 15 May 2020 19:15:22 +0000 Subject: RE: [PATCH v2 09/10] x86/resctrl: Add arch_has_sparse_bitmaps to explain AMD/Intel CAT difference To: James Morse , Reinette Chatre Cc: "x86@kernel.org" , "linux-kernel@vger.kernel.org" , 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> <980a693a-b823-96e1-9b4f-d7bbf4f09714@amd.com> From: Babu Moger Message-ID: <1cc88f7f-0f40-aa1d-1d8a-59cc8053e474@amd.com> Date: Fri, 15 May 2020 14:15:18 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SN4PR0801CA0024.namprd08.prod.outlook.com (2603:10b6:803:29::34) 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 SN4PR0801CA0024.namprd08.prod.outlook.com (2603:10b6:803:29::34) 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: zbnrgfp9Yea60Ix51jfeJq5tNbtgtKbR1R55Ge2FY4zpmXlIOz/lykZdpfrOlN7cBhE5++IdbAF6oYLhe3piKMAyVX+NVo44XQicQakjEsrPE5Z5GM5TVLB6S/1RUTqs0UU0Wcix6vbe7Ql9sKGQdeDyVhc4vb3dlDumNnJTnmpeP3XJ0I/hNBP7UmVsbIR9sRFZR25o3uUFf1EpgUtO+2qEjHnBsmNH6wSGcUojQ885SrpEUZMjMSHa16/HXM/nww+TbGeiE3JE3BIr/mx7MwqVUpGtQesyVSFt0qinbUuJr/mKSawaqP7yWDZg/tj2OPWf6iOF1iuziZ9py53eP1K/h64xImNiEVwSvrFj1gZzWunFKvexnjBXO15mkRY0EsKB/ISZEUlMMm2gQceeV5pCC5QG1zH/DXaxImUcdUxqHko7StxNTFcXB2CKRtNzYIkzWOWhQJEji9HBEOS5luRrrEplQ6+xhJcK1/ah/m4= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 79ae5e46-1aa0-49bd-c442-08d7f9045078 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 May 2020 19:15:22.4000 (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: v/jRtAFiYjz3yzaYBhjO6A3rGcAJIBoPL27cvtgjh/7ET5sIFgnYkyVn9sGM+g7Q X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN1PR12MB2430 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: James Morse > Sent: Friday, May 15, 2020 1:22 PM > To: Moger, Babu ; Reinette Chatre > > Cc: x86@kernel.org; linux-kernel@vger.kernel.org; Fenghua Yu > ; Thomas Gleixner ; Ingo Molnar > ; Borislav Petkov ; H Peter Anvin > > Subject: Re: [PATCH v2 09/10] x86/resctrl: Add arch_has_sparse_bitmaps to > explain AMD/Intel CAT difference > > Hi guys, > > On 13/05/2020 21:03, Babu Moger wrote: > >> From: Reinette Chatre > >> 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 > > top -> to > > >>> 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? > > It does... > > > > That is right. AMD allows L3 mask be all 0s. I will be great if this > > property can be indicated it here. Thanks > > Ah, this is a bug I didn't intend to introduce! > > Intel has: > |       if (val == 0 || val > r->default_ctrl) { > > Whereas AMD: > |       if (val > r->default_ctrl) { > > > So this empty bitmap is permitted today with resctrl. (and, its another try-it-and- > see). > > I'll add an 'arch_has_empty_bitmaps', I don't think overloading 'sparse' to mean > 'sparse > and empty' is a good idea. Sounds good to me. Thanks