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Received: from BL1PR12MB5320.namprd12.prod.outlook.com (2603:10b6:208:314::17) by DS7PR12MB5743.namprd12.prod.outlook.com (2603:10b6:8:72::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.592.11; Fri, 6 Nov 2026 21:25:54 +0000 Received: from BL1PR12MB5320.namprd12.prod.outlook.com ([fe80::1876:4a6d:2cf5:b8d1]) by BL1PR12MB5320.namprd12.prod.outlook.com ([fe80::1876:4a6d:2cf5:b8d1%5]) with mapi id 15.21.0592.010; Fri, 6 Nov 2026 21:25:53 +0000 Message-ID: <39598840-29b1-4524-806f-9ef9dc2a3944@amd.com> Date: Fri, 6 Nov 2026 15:25:51 -0600 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 4/5] selftests/resctrl: Use bandwidth values for AMD MBA schemata To: Reinette Chatre , Swapnil Sapkal , tony.luck@intel.com, fenghua.yu@intel.com, shuah@kernel.org Cc: Dave.Martin@arm.com, james.morse@arm.com, peternewman@google.com, eranian@google.com, tan.shaopeng@fujitsu.com, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, x86@kernel.org References: <20261022132517.46805-1-swapnil.sapkal@amd.com> <20261022132517.46805-5-swapnil.sapkal@amd.com> <4f656f59-9f2c-4774-9d9b-3a4d7b7b509d@intel.com> Content-Language: en-US From: Babu Moger In-Reply-To: <4f656f59-9f2c-4774-9d9b-3a4d7b7b509d@intel.com> Content-Type: text/plain; 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The >>>> + * test sweeps the bandwidth from 4 GB/s to 40 GB/s in steps of 4 GB/s, >>>> + * which the hardware represents in units of 1/8 GB/s (i.e. 4 GB/s -> 32, >>>> + * 8 GB/s -> 64, ... 40 GB/s -> 320). >>>> + */ >>>> +#define AMD_ALLOCATION_MAX    320 >>> >>> The AMD maximum is enumerated from hardware. How can it be ensured this is >>> the appropriate maximum for all AMD systems? >>> >> >> As Babu mentioned, it's difficult for a single-threaded workload to >> reach the hardware-reported value. For that reason, I used these >> values to verify whether throttling takes effect. > > Just to confirm, my question was not about needing this value to be the actual > maximum of a system. Instead, I just wanted to confirm that this "320" value that > is hardcoded here for all AMD systems is a _valid_ value. Since the actual maximum > value is enumerated from hardware it is not obvious to me that all systems will support > this hardcoded maximum. > The value 320 corresponds to 40 GB/s. I have tested this on several systems and was able to achieve the expected 40 GB/s bandwidth. The tests did not fail. There are some older systems where the test is not expected to run because AMD UMC support is not available. If you are concerned, since we are no longer depending on the maximum value, we can be conservative and start with the following adjusted values: #define AMD_ALLOCATION_MIN 32 #define AMD_ALLOCATION_STEP 16 This allows the value to reach 32 + 16 × 10(num_allocs) = 192, which corresponds to approximately 24 GB/s. Hope this answers your question. Thanks, Babu