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Fri, 14 Nov 2025 18:51:28 +0000 Date: Fri, 14 Nov 2025 10:51:26 -0800 From: "Luck, Tony" To: Dave Martin CC: Fenghua Yu , Reinette Chatre , Maciej Wieczor-Retman , Peter Newman , James Morse , Babu Moger , "Drew Fustini" , Chen Yu , , , Subject: Re: [PATCH v13 12/32] x86,fs/resctrl: Support binary fixed point event counters Message-ID: References: <20251029162118.40604-1-tony.luck@intel.com> <20251029162118.40604-13-tony.luck@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BY3PR05CA0032.namprd05.prod.outlook.com (2603:10b6:a03:39b::7) To SJ1PR11MB6083.namprd11.prod.outlook.com (2603:10b6:a03:48a::9) Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PR11MB6083:EE_|DM3PPF8F79256C7:EE_ X-MS-Office365-Filtering-Correlation-Id: a595a587-b543-4fff-97d1-08de23aed179 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?Xo/hf9jzGOuLJvGSi39O1hcxdnhJMFc9/YKQytX8lGQeK3jv+LL2y8qFvarC?= =?us-ascii?Q?K7g1ykS55okOJ03yksVJTVTdE9o1gFOG8Ll2eLNDI8sZuyrAxb94AtxLjhHD?= =?us-ascii?Q?a6cHJ5Qx7m6dg62JHUo3TJ9uzRSlGy+7czO2pCK3aq3arRtT+1pP//IFqNBx?= =?us-ascii?Q?3LzCxaVrhsv0dzgd0I5TAMa/ghI3c0rdOrL2Kc+0bdFsbhoUuf4iqbhwGe+C?= =?us-ascii?Q?puRiPpKMVpuTiCxzXVRY/cFqfnV2miYIMV+glMlOnWMwavlA+a4LtwPQAamJ?= =?us-ascii?Q?4TSAdlEjQkbfZhjiBtLmJQeMXHZsIXbsjpld7cr19f22uHm09n3ioMIFPG3J?= =?us-ascii?Q?sNIZW3i5V93vwblIyvlXImDFKsGW4HCn4xfcj36ZXqfxA/mDK/yicvs69XJ5?= =?us-ascii?Q?vtecnAfaUl31pBLhRZnDw/if+buP5dnRvYggzWYRh2Yi3QwWQMkzml7dy10m?= =?us-ascii?Q?i+Q3RHsB524A5sBd2vMWCIYtyvD/oyOsjlLLsywiAPGsvt9QfZJI6rjTt2wy?= =?us-ascii?Q?Q6h3VSnU7x3z3W6De9vSJsaWC5isDT+lgD1a52rzCWx4JVM3Gp/Q5Zo7Oao/?= =?us-ascii?Q?usBwIqFORZXep0+rdE2em2C6TAPzIf2Xzj9BeT77kAjtndLszYXdUL7EcZnA?= =?us-ascii?Q?B+3XmTcBJk0g/0IN+k0O+x+XzGBrF45wmX/wrFGQd4UpqmgGU9Ef1KWtPeg9?= =?us-ascii?Q?+cMUcsp0bCWg8BXMhw3ookiWOyf0KFpQlj5cehySJ4domyC6V/6dGRGGVHTx?= =?us-ascii?Q?FPxnGVDXW0/SVT9IlWpX1CkINjp993Ht2FB7aKz9A8pYdJD6C1bv/g0k60xP?= =?us-ascii?Q?cTpdjX/2a+y/iB8xEEF+mKp6/9+/DF64y9Blu9Zfk+oBifvTzWvjksmjy15I?= =?us-ascii?Q?qd7HCVqXgArOoecdHGIwXnOtDlMApBiIeNG9euUn7gt8lVhlsSh0Di4Div84?= =?us-ascii?Q?bdg1ClAdOgSpyWN0IWQgLSe3yKAsHNNUSD80Red8PhjI0aHV+iTCFqwSGGVJ?= =?us-ascii?Q?mLzdQmC9JIYq5sADQNlYsx6so6BkYPJd6k4h5Cgxqi2+NLN2UZdm9oBq0jN6?= =?us-ascii?Q?ME62O3M6H32TjZFBwAHtlOwvVI64Dwh9Yk6PWR7wHLvE7aEWd8bBmC+o7Dwt?= =?us-ascii?Q?Bj4iW7fY7GXV6G32z7enEMTuGELqVF4683vgfph39CPMM242egbxQyfpdnNh?= =?us-ascii?Q?K1dMSBeuQK+LTpcg7YrskxMdum+bZ14WmvqBtgs7QenYI3p89Toh+jEUFtZ8?= =?us-ascii?Q?+1/4tomrP4UkoIIfodrh4HLqCJ9w0zjAIxhoFCyeCVJQGeliVdHfn7WN74fR?= =?us-ascii?Q?lz52CpfE71otULcbnmwNgB1MZVWflJrz5l6AbfaqmHqGBck6eSnBcY919AuS?= =?us-ascii?Q?xT82lLefK/55e4wfZUyTQdYErpZ68szJ2Wk8+U6i048xbppgzbFnETv1fLZe?= =?us-ascii?Q?SgwXhRhbmOtgiD4gchGwsDm+SFFGDgyd1jlpYcZ3m2Zj1fOkvh9NX3EOm4Kn?= =?us-ascii?Q?Ikeko1CP8zRZLoImx7e5UO4ZKg5XXrvOHOYxmOFq2YZobygDiAK0V9qevnIT?= =?us-ascii?Q?0rqVJuxzqrzyZjj8wqrTpJmJSgwVCa4K6DMkwYYz?= X-MS-Exchange-CrossTenant-Network-Message-Id: a595a587-b543-4fff-97d1-08de23aed179 X-MS-Exchange-CrossTenant-AuthSource: SJ1PR11MB6083.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Nov 2025 18:51:28.1041 (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: Dh7FOxws9IRKQPyvwvTwmMiA6zzhacDgk9SmBVjRz/bEZPgGAK/vhAS+rOxBiX90KsRALneUJtS9ooOwxQzbJQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM3PPF8F79256C7 X-OriginatorOrg: intel.com On Tue, Nov 11, 2025 at 05:16:22PM +0000, Dave Martin wrote: ... snip > > I'm not a fan of the "floor" option. Looks like it loses precision. Terrible for > > Loses precision, but does not advertise bogus precision precision > beyond the precision in the original value. (This is why it is not > standard to print doubles with more then 15 significant digits, even > though 17 significant digits are needed for bit-exact reproduction.) > > I don't know whether this matters relative to the use cases, but it > would be nice to have some rationale. > > > 1-3 binary bits. Also not what I'd like for the bits==18 case that I currently > > care about. > > > > "ceil" is good for bits > 6. Almost matches my numbers (except I jump > > to one more decimal place one binary bit earlier). > > > > What do you think of me swapping out the values from 7 upwards for the > > ceil values and documenting that 0..6 are hand-picked, but 7 and up are > > ceil(binary_bits * log10_2)? > > If there is sound rationale for hand-picking some values then yes. > > I haven't yet been convinced that there is ;) I don't have a rationale and I've been doing the thing I tell others not to do "getting attached to code that I wrote". I will switch the whole table to the ceil(binary_bits * log10_2) values. One exception for binary_bits == 0. Back in the v6 version of these patches I printed as a plain integer. Reinette commented[1]: At this time I understand that it will be clear for which events user space expects floating point numbers. If the architecture in turn does not support any "binary bits" then I think resctrl should still print a floating point number ("x.0") to match user space expectation. -Tony Link: https://lore.kernel.org/all/8214ae1f-d64c-496c-b41d-13b31250acea@intel.com/ [1]