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Shenoy" , Naresh Solanki Cc: Huang Rui , Perry Yuan , "Rafael J. Wysocki" , Viresh Kumar , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20241219192144.2744863-1-naresh.solanki@9elements.com> <057d8f01-c1ee-428c-8c19-80edcf9017bd@amd.com> Content-Language: en-US From: Dhananjay Ugwekar In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: PN2PR01CA0001.INDPRD01.PROD.OUTLOOK.COM (2603:1096:c01:25::6) To LV8PR12MB9207.namprd12.prod.outlook.com (2603:10b6:408:187::15) Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9207:EE_|MN2PR12MB4317:EE_ X-MS-Office365-Filtering-Correlation-Id: 1b898370-2665-43bd-f1db-08dd2f997e23 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?a0dlalVhRCtYSExtUUZyNThsMGVQUmkwc1pKZFk1WTh1UmF0QUFYZzhpNmtY?= =?utf-8?B?L2FhNmVheSszOFVpK0NlWGYzNm5LNFJDVlRiS3VTTkFGYVMrVjZ6c0daOU8w?= =?utf-8?B?YTRRSWJTTlNuK1dVcFU4bktVTHRISWZUYkhzcXB6d3pSajB6ZlJQSXdEMU1h?= =?utf-8?B?cTBYdS9KTWFya0ZXMnlCbzByRCtXUUxCcldtSm5OYk1na1dkZ0xuSTZjSCsx?= =?utf-8?B?NGd0VW1saGtUR0NXaW04UWh1M1pFQVh3SS9RdXorMTZXbWlLMlBJK2lDU2dT?= =?utf-8?B?bEVrN2VwSHZsYVVOMWhKMnBncFZmbTh1MzFUUHl1M09ocW9xR3hHMzdJN3Uz?= =?utf-8?B?cjFmSndmMFpsc3JOTWJ5cm5pbmNxNkM4VmRvMk1mM2Q2czRkMlM3U2RLMEVV?= =?utf-8?B?M2Qrcjl6NVJFYVRzZEZYeUVQZWNnSFFVQ1BGL3k1RTdMRHkxUWVXNkdhTXFE?= =?utf-8?B?Y29UdWpCLzRvZERmaWhpV29aS0thMUExQkZ0anBRdVZOeHk1QTNpRUcwcFpj?= =?utf-8?B?RnlDK2ZqZElreGV1Nmd4VkttMEM5eFkzc1lySnZDQ3dnQU5YVlcyaCt2NUx0?= =?utf-8?B?a0FVVWVaYmQ4WnU2WDBRTENab2t3VUZtb0Z0S0RnNjRzdnQ4bHRsNjRiRnFu?= =?utf-8?B?QjcxdTZrNHYwa2VLSDhXY0lKb05kM2xnNHViODJ3K3lxeDMwRW1Yak4wMlds?= =?utf-8?B?bXJXWi81cFRDQTFoTU5QR0RVN2pwWUlucXF1SG01Vno0ZFdzVEp0T3hEb2J6?= =?utf-8?B?WTMxYUJmeWJmWVNIbGl5M1MwZTd4TGJZeVVWZGU4TGlFNWFKUE90UjRqRnlv?= =?utf-8?B?U2MrUEl4clN3OUdqVFFOd2VRRkFBWjVxQ2J0K0pjZmZ0eUlJVFVieWpPMWpT?= =?utf-8?B?VVZ3aGJFQU1BenNkS0Izb1V3dUZtWGRsM29ERHcvejhsZ3ZGNmNDQzVzaXcx?= =?utf-8?B?cTgxbnduelNxeEUzdG1vYmt4WGw3NTVIUnRRazlDd3hWRm1SN2Qrd2gvdWs3?= =?utf-8?B?NTZUK2V3WnoyWmh5WkcyME0waE9HRGMxdHNBNkZhOGtoL3lHSVh1aXZmQUd6?= =?utf-8?B?NWpEMlRNWmlFOFVheGVWeTZ2UGZLcERzREhjYk9DQ2dVaFNTMS9LRzdzZ1BI?= =?utf-8?B?TURrZDVVV3ZnWE9HVXhsbCttNnpCdHQzdUV1RnF1bmR3QTUzV2NWY09qY1d0?= =?utf-8?B?M3VGN3pzWllLWHRMeHo2K2tYSTgvMUJscTg4R3hGVWRlYlBwMnNMZXZPdjV2?= =?utf-8?B?WXNNTmRtc2hWWXluRDd2cW1oRDRMMG9RNmoyeG9wZ2FpS0xKaTFUbzI2SXMv?= =?utf-8?B?bkN4OTlGRzhjdHBmQjRHSlQ4RndxZk82aDJyNk1VZGxaRFE3aUQ4UVVLWGtL?= =?utf-8?B?SHo0eGt0RGdMMm1xUmQ1SEZGZmhGc1ArRWcyeS9TSEtRbnR4cjJVYTdiVmNj?= =?utf-8?B?dWpnNk0zMEJpMGNuM1RSM1kvOTFYa2NPY1FrbHVSbEtqaEd2amxBMzlJL0J3?= =?utf-8?B?SitXU2pMdGZBSFBoSUhrandEQ1ByUFQzN3hsRzNrdHhlTDdpU2Rzam5LaHZp?= =?utf-8?B?dmo2elVNTEFzOHpUWXNYR0pqVGFuOElxVXRLdTRnN2xPcm40Y01LODNpWUJK?= =?utf-8?B?eC8wRDNLN1dTd2FJR1pYeUtyNFhPV0FmNTBLcThBM0E2YnE4ZldLMElzNEM2?= =?utf-8?B?MXdrRmRwT0xLdVFTRllkQlk3ekIxdlNybU9PNDlKSnZTOGIzWHo1aW8xNElE?= =?utf-8?B?eGZqb0UyaklDdy8xM3RzM3U4b2FRbjYyZ1YwZ25GNWE4RW56WGc2Q2J1enM3?= =?utf-8?B?dTdOUFU4dnAyV2hUb0FMUT09?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:LV8PR12MB9207.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(376014)(7053199007);DIR:OUT;SFP:1101; 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Shenoy wrote: >>> On Fri, Dec 20, 2024 at 12:51:43AM +0530, Naresh Solanki wrote: >>>> The previous approach introduced roundoff errors during division when >>>> calculating the boost ratio. This, in turn, affected the maximum >>>> frequency calculation, often resulting in reporting lower frequency >>>> values. >>>> >>>> For example, on the Glinda SoC based board with the following >>>> parameters: >>>> >>>> max_perf = 208 >>>> nominal_perf = 100 >>>> nominal_freq = 2600 MHz >>>> >>>> The Linux kernel previously calculated the frequency as: >>>> freq = ((max_perf * 1024 / nominal_perf) * nominal_freq) / 1024 >>>> freq = 5405 MHz  // Integer arithmetic. >>>> >>>> With the updated formula: >>>> freq = (max_perf * nominal_freq) / nominal_perf >>>> freq = 5408 MHz >>>> >>>> This change ensures more accurate frequency calculations by eliminating >>>> unnecessary shifts and divisions, thereby improving precision. >>>> >>>> Signed-off-by: Naresh Solanki >>>> >>>> Changes in V2: >>>> 1. Rebase on superm1.git/linux-next branch >>>> --- >>>>   drivers/cpufreq/amd-pstate.c | 9 ++++----- >>>>   1 file changed, 4 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c >>>> index d7b1de97727a..02a851f93fd6 100644 >>>> --- a/drivers/cpufreq/amd-pstate.c >>>> +++ b/drivers/cpufreq/amd-pstate.c >>>> @@ -908,9 +908,9 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata) >>>>   { >>>>       int ret; >>>>       u32 min_freq, max_freq; >>>> -    u32 nominal_perf, nominal_freq; >>>> +    u32 highest_perf, nominal_perf, nominal_freq; >>>>       u32 lowest_nonlinear_perf, lowest_nonlinear_freq; >>>> -    u32 boost_ratio, lowest_nonlinear_ratio; >>>> +    u32 lowest_nonlinear_ratio; >>>>       struct cppc_perf_caps cppc_perf; >>>>         ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf); >>>> @@ -927,10 +927,9 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata) >>>>       else >>>>           nominal_freq = cppc_perf.nominal_freq; >>>>   +    highest_perf = READ_ONCE(cpudata->highest_perf); >>>>       nominal_perf = READ_ONCE(cpudata->nominal_perf); >>>> - >>>> -    boost_ratio = div_u64(cpudata->highest_perf << SCHED_CAPACITY_SHIFT, nominal_perf); >>>> -    max_freq = (nominal_freq * boost_ratio >> SCHED_CAPACITY_SHIFT); >>> >>> >>> The patch looks obviously correct to me. And the suggested method >>> would work because nominal_freq is larger than the nominal_perf and >>> thus scaling is really necessary. >>> >>> Besides, before this patch, there was another obvious issue that we >>> were computing the boost_ratio when we should have been computing the >>> ratio of nominal_freq and nominal_perf and then multiplied this with >>> max_perf without losing precision. >>> >>> This is just one instance, but it can be generalized so that any >>> freq --> perf and perf --> freq can be computed without loss of precision. >>> >>> We need two things: >>> >>> 1. The mult_factor should be computed as a ratio of nominal_freq and >>> nominal_perf (and vice versa) as they are always known. >>> >>> 2. Use DIV64_U64_ROUND_UP instead of div64() which rounds up instead of rounding down. >>> >>> So if we have the shifts defined as follows: >>> >>> #define PERF_SHIFT   12UL //shift used for freq --> perf conversion >>> #define FREQ_SHIFT   10UL //shift used for perf --> freq conversion. >>> >>> And in amd_pstate_init_freq() code, we initialize the two global variables: >>> >>> u64 freq_mult_factor = DIV64_U64_ROUND_UP(nominal_freq  << FREQ_SHIFT, nominal_perf); >>> u64 perf_mult_factor = DIV64_U64_ROUND_UP(nominal_perf  << PERF_SHIFT, nominal_freq); >> >> I like this approach, but can we assume the nominal freq/perf values to be the same for >> all CPUs, otherwise we would need to make these factors a per-CPU or per-domain(where >> all CPUs within a "domain" have the same nominal_freq/perf). At which point the benefit >> of caching these ratios might diminish. >> >> Thoughts, Gautham, Mario? > > No; in this day of heterogeneous designs I don't think that you can make that assumption, so yes if we had helpers they would have to apply to a group of CPUs, and I agree at that point the caching isn't very beneficial anymore. > > If the main argument is to make it easier to follow we could have some macros though? Agreed, I'm working on the helper functions patchset, will post it shortly. > >> >> Thanks, >> Dhananjay >> >>> >>> .. and have a couple of helper functions: >>> >>> /* perf to freq conversion */ >>> static inline unsigned int perf_to_freq(perf) >>> { >>>     return (perf * freq_mult_factor) >> FREQ_SHIFT; >>> } >>> >>> >>> /* freq to perf conversion */ >>> static inline unsigned int freq_to_perf(freq) >>> { >>>     return (freq * perf_mult_factor) >> PERF_SHIFT; >>> } >>> >>> >>>> +    max_freq = div_u64((u64)highest_perf * nominal_freq, nominal_perf); >>> >>> Then, >>>          max_freq = perf_to_freq(highest_perf); >>>     min_freq = perf_to_freq(lowest_non_linear_perf); >>> >>> >>> and so on. >>> >>> This should just work. >>> >>> >>>>         lowest_nonlinear_perf = READ_ONCE(cpudata->lowest_nonlinear_perf); >>>>       lowest_nonlinear_ratio = div_u64(lowest_nonlinear_perf << SCHED_CAPACITY_SHIFT, >>>> --  >>> >>> -- >>> Thanks and Regards >>> gautham. >> >