Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.35 as permitted sender) client-ip=23.128.96.35;
Date:   Tue, 19 Sep 2023 08:50:33 +0200
From:   Maciej =?utf-8?Q?Wiecz=C3=B3r-Retman?= 
        <maciej.wieczor-retman@intel.com>
To:     "Luck, Tony" <tony.luck@intel.com>
CC:     "Shaopeng Tan (Fujitsu)" <tan.shaopeng@fujitsu.com>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "Peter Newman" <peternewman@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <skhan@linuxfoundation.org>,
        "x86@kernel.org" <x86@kernel.org>,
        James Morse <james.morse@arm.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Babu Moger <babu.moger@amd.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "patches@lists.linux.dev" <patches@lists.linux.dev>
Subject: Re: [PATCH v5 8/8] selftests/resctrl: Adjust effective L3 cache size
 when SNC enabled
Message-ID: <7gbxb6kxwa6anvcc4dquyuu7yronww6ztelazn2xllplorhbp5@i7o4fum5tjuf>
References: <20230722190740.326190-1-tony.luck@intel.com>
 <20230829234426.64421-1-tony.luck@intel.com>
 <20230829234426.64421-9-tony.luck@intel.com>
 <TYAPR01MB633033C489AAC0E514CBC6688BEEA@TYAPR01MB6330.jpnprd01.prod.outlook.com>
 <SJ1PR11MB60839EB5CC3D172D864DF7A7FCEEA@SJ1PR11MB6083.namprd11.prod.outlook.com>
Content-Type: text/plain; charset="utf-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <SJ1PR11MB60839EB5CC3D172D864DF7A7FCEEA@SJ1PR11MB6083.namprd11.prod.outlook.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?elg5NFRpMXNVZEhpYU1icWVqcVN4TTh0TWh1V2x5V1VMWmdKa3NaTEFKUnR5?=
 =?utf-8?B?cVVoTVp6ZXh2a3RRdE5seStKck1PeTFyMnpTcnlpQW1PTHZ6UkhDUnYwZGRX?=
 =?utf-8?B?OFhTc3N3VXFYcmc4VmtPM21xTTdzeWkvbDd1OThuUGFUM2cybWhFK0s2ZUJn?=
 =?utf-8?B?UTQvQy8vcFR1TUFCdnEzUVJYU214VUpIdHFlOHdzLzJaTExDYkpNc2NRM2RL?=
 =?utf-8?B?R2lseW5jMGYwMnFGTjlaeTREYnF2K1dWbWJaVkE3RjVFUGlsMTBndlJrQ012?=
 =?utf-8?B?YnJ2c3U4YnhQcTFRelErTmdRWFYyYzhJYUVIZzBUb1lMaW5UUzg1MlFXdytE?=
 =?utf-8?B?Vy85QVNRU1ZycnUwR1VNeUI5OTdFMU53NG1aVituNEsrMWFxd1grS25MU21p?=
 =?utf-8?B?bGl5aWZJY00vbmRoZ0JLMVoxR2xhV2M5NWJ5ZjZ0YmtJVmNLUkJFakQ4RDBX?=
 =?utf-8?B?K1dlOGR0M0Izd2VpeGlNR2ZOeDBVUzBZaEF3ZDE5QUw2U3A1bXBYMENtaisz?=
 =?utf-8?B?Q29Vc1Q0Yjk5ZVFCdUtNbkhvVUthUC90UmFjbTZFV0MxK3lRSE80L1dCRU45?=
 =?utf-8?B?NE45NUJoWnBGd1pWWkE2aXdCSjRZaWJ4UjcrcEZEL0ZFb2FCLzB4ZGZ1cUtE?=
 =?utf-8?B?dzZyOHJwVWdZMGhyRy9td2g2YStRajB0Um45d0xYQTJVNFRSVkZVSENEMHZT?=
 =?utf-8?B?Z1pmSFZaNlluUkFWWDIzZlY3VUNaWUduMVluZnNMY25TU20wampLOGVGUlZp?=
 =?utf-8?B?a2Z5cGcwUWpTRFNhSzMrV0VmMXdySG9mL1VPQXNkbWR0ZlpVbHVieE11NHJu?=
 =?utf-8?B?SkRSdVJwWjM3NEtQUTJQWDNqaTloOG1uUHhSVTR5azdQWjJYSWZVYThTK2ZC?=
 =?utf-8?B?bjlLbU1NN3NWL0UvUFRwOWJyWmtjZVZKVGwxWHNrMGVtT3ZzQ1piZHJzdVN6?=
 =?utf-8?B?MlRwSU1hejZxZEpRMVd4MTlCV3ZMUUJJTTNpTGQxblVaM2hvNnJIRDV5eTlE?=
 =?utf-8?B?cW1EeDJXMjNTQndmUDNCUGxiNzFxek0yVmNla3RzT3pQMzd2bkRZalVOd050?=
 =?utf-8?B?RkE3QW9CdEJpbWJta2tpdi9PREc3VlY5TUN3Zmp4eVQ2TVhZWm4wTGxxc2lC?=
 =?utf-8?B?aEFMeG13MmFTdTRKcWhtRGxNMTN3UzMyeGhoS01Wb0hDV1FFTHNRaFM4VEI0?=
 =?utf-8?B?RDlITi9mYkhRVVhwUEVxRjBzek1sMjdOUXVxM2QzNUpoaTNlVkpnRHRHMmlT?=
 =?utf-8?B?S1VnUzFoL210enZFbjlDNUZhdkIrWGlTOWF2QXlKNnUrdzNBYlRWRDY3NHhn?=
 =?utf-8?B?WW5kNzNxaHhudkl4OWtNdjFGb1cwaFlLRTdOV0h0RUZzajN0Rjc0Z3EvV1F3?=
 =?utf-8?B?OGVobDVyRlUxaE1MbG4rTHd2UTU3c0oyT1B1enB4TmR2TGVWSldDZ3NMSkhB?=
 =?utf-8?B?SW5YckVRa0N3MWdCalNQdkxqcEw1T2lhbDlGL0JVYU94OXJmVFJuNnBON0o5?=
 =?utf-8?B?bmIxWUNNNkFnZWxBZi9pbmRrMXV1RnY0RzBBS2J4STJxMUxRWDBVbUgxTEZo?=
 =?utf-8?B?KzRFWVNvakV0SE4zNjcydXpyQmM0akRtMWx6L3JkeFNidmJPWWtvQjMzRUZK?=
 =?utf-8?B?cHlDRW1NVUhuNWN5L3BiNEh1aDRZUlJKY3lqYVcwc3pJR2xnWDcxcDZuRTFR?=
 =?utf-8?B?MXluQWJHR2ROTDF0Vk5pWlpFSy8yVEdnOWpOZUFlc0FtOXpFdFRkZ2hFNytv?=
 =?utf-8?B?K1d4Y01xdUcyd2RvVGZKK2RRWEZWeHlXNTYxaTJ2Z2J2d3BLTG0xRFpURXM5?=
 =?utf-8?B?Nm43czdUN21JSHh4ZGhzaFJXSWxJVU5KaFV2dnlWTTBVVnlmWkpaeFV2ZXd0?=
 =?utf-8?B?Q2tOdThlNEl5MWRLZEhCQjVTUHNzb3ZYK2gwQXZKZFRPRGprQXRLNlFyalM4?=
 =?utf-8?B?cGp1b0ZRUmRPQ21jOUNTUm80NXQ3WXJudThkVWcveXhtQTg3Mkh1L05tSU9F?=
 =?utf-8?B?M0dpNkxUMmJJamFUSUlEMnJHeGlWbTJqWHNuUFBXZmVNeXFVN1NuRFIxR3Jm?=
 =?utf-8?B?M2xsTXo2ZG94ZmRGbXFyQTNIMllmai9xS040WTZsUzI2RWIxMlZFYi80ZkdF?=
 =?utf-8?B?KzhJNVZKUkhYWHFJa1ZQTkNnQzRXS1JXUGc3cDlyc0ZnTEFSUUdINkFFS0Nl?=
 =?utf-8?Q?leuwu9/euC1+jz3gkZQBM0A=3D?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 67402029-5f4c-4666-4a14-08dbb8dcbd30
X-MS-Exchange-CrossTenant-AuthSource: MN0PR11MB6231.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Sep 2023 06:50:41.1969
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: znWrT1CPvtsxverZtRw4jWUy+eI5a6ci52PJvUqLrMZ9+x/Y3hkPtrkP4Hy0BWAC4gT6Fw4KaQw341KOEsSPvgs3U4mhkWYZTJS2c17hFbk=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR11MB7842
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable
	autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on groat.vger.email
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (groat.vger.email [0.0.0.0]); Mon, 18 Sep 2023 23:51:06 -0700 (PDT)

On 2023-09-07 at 16:19:37 +0000, Luck, Tony wrote:
>> > +   if (4 * node_cpus >= cache_cpus)
>> > +           return 4;
>> > +   else if (2 * node_cpus >= cache_cpus)
>> > +           return 2;
>>
>>
>> If "4 * node_cpus >= cache_cpus " is not true，
>> "2 * node_cpus >= cache_cpus" will never be true.
>> Is it the following code?
>>
>> +     if (2 * node_cpus >= cache_cpus)
>> +             return 2;
>> +     else if (4 * node_cpus >= cache_cpus)
>> +             return 4;
>
>
>Shaopeng TAN,
>
>Good catch. Your solution is the correct one.
>
>Will fix in next post.

I played around with this code a little and I think the logical
expressions are returning wrong values.

On a system that has SNC disabled the function reports both "node_cpus"
and "cache_cpus" equal to 56. In this case snc_ways() returns "2". It is
the same on a system with SNC enabled that reports the previously mentioned
variables to be different by a factor of two (36 and 72).

Is it possible for node_cpus and cache_cpus to not be multiples of each
other? (as in for example cache_cpus being 10 and node_cpus being 21?).
If not I'd suggest using "==" instead of ">=".

If yes then I guess something like this could work? :

+     if (node_cpus >= cache_cpus)
+             return 1;
+     else if (2 * node_cpus >= cache_cpus)
+             return 2;
+     else if (4 * node_cpus >= cache_cpus)
+             return 4;

PS. I did my tests on two Intel Ice Lakes.

-- 
Kind regards
Maciej Wieczór-Retman