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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?J7WuOgqaCdI0DG7OzCOv02xL+5OU0S0YQ+yAugY+gVq0Ld7Iidd9fKWurZb8?= =?us-ascii?Q?xpeUXJGrelIgAxn0bj2mpctAQvgF+oqAtlJ85GNLjRYXTTcRyXKlmjq+lWc2?= =?us-ascii?Q?nKsVUev1YlnQErJTOieVWm3YW7eORkkie2s3fgXzdgt0KsvLTTFb9pnDT/jL?= =?us-ascii?Q?lvkhsvP+ADnD3fgbqcTqP4HjbJa6ONSnB04rqpf1S/q0PD3QrGncHCD7DQIU?= =?us-ascii?Q?86vfnj3vi7iuOFIpNrugg7N2QEjC3nC5/lNt+Ycp3LlkD3+I4GslFyNyTiiv?= =?us-ascii?Q?UDUh08lOr0wkqBcIV1sAQa70ncQaSdxtMOgLaZCRJFdyllkCWhnk9KRqY77c?= =?us-ascii?Q?flcEciUFVPEkPWPbUPVxpSWOXe2lRezL93fs8/rvQWwiyvWsyiiGUM9D8cXv?= =?us-ascii?Q?b4HnggJSnPLF7otP3zmMTtrJVdSBZy5iuPKLeEuruXl2SwhqDznh55g0qv0x?= =?us-ascii?Q?f9uda3M2ggGVjRorXiyMnbc5dq1oNyhTBNNwVYv1o+ABMRGIGgtALN7WUJ8m?= =?us-ascii?Q?cnh2/TLe8mc1UZta5db6KNzkr3xYVRgjvzxflJpC/3Jl+a7OjKztzjUeuJtZ?= =?us-ascii?Q?RCrPW0Jo+tj0Nskj1Lh+GmdFKlMDU8fgOtLd9UW8mDg511lqVANR35DFApB2?= =?us-ascii?Q?xyStd5o3e7fdR+3lh/v+uZNF8u9R0+Vqoyn8QBvSap1K0lG01mtyuaGJaCog?= =?us-ascii?Q?KRYl7RY9+jx8T/ZEoN0Xq69oSUFE0wTzVJI9ihYkYKOjCtDWMoWWHT6j181M?= =?us-ascii?Q?od1OoBzLHYILrTuCF8wNTPcOn+Z9Iq4cAwmO7GeOE0TWFVzefiX8PLXH/d3b?= =?us-ascii?Q?X18nzZdM21f//n1NywhXEBb/6EKhlDGhFAGZzu3Bho+FGBpyrJe0aKbvL8n+?= =?us-ascii?Q?sEwbqk7OpyAjko8Qyg6Q/FTDDWOUa3z8QS/qln62geLJgAvj23WLnpU/1oVC?= =?us-ascii?Q?ScuVSW8grm4AcsNFILw/gRbTPHljBq4IfWgJssPyqE5IqkAUgVh/JCEQg1Bq?= =?us-ascii?Q?djmJYbk84bDE8ETo+1D+J0ipGfVaKineK2VqWoSdSrQFcLrxCP/y17/UQqkI?= =?us-ascii?Q?A9qOKwUZE44Bxfb3iOx+4AfJhuH5rPLc7JSTXGVdpoCKqT7li1i2vEnh2wld?= =?us-ascii?Q?y64DdqFCuEbwGxE8S734GlmI1EVGDG4nrD8WylYSBmq1McORdS0rE12CpAb9?= =?us-ascii?Q?4aMfjtD7FDZEGn7uDP6MxxKCDixyT7a2HbpAFmLzGCRD5eunJiVVGbjweLes?= =?us-ascii?Q?rc/NjhUW5ToZxKMBo71vx9kg3H4DQOJwVE2m0zDIiNlm8IxwUD/cRfiQ9rBp?= =?us-ascii?Q?m3Pl7aXiIluPPUaxY/lOixQ/rz5Ze2+EFjw+U5AUz51KoPcTCQ7XJ7ZNgpQW?= =?us-ascii?Q?WHAzVt4IoQ4XZ+TLLTcAqZ9cNbiJmPKSgTk9+NtfddkbmZzZnbystjyVwRvm?= =?us-ascii?Q?7HBVdchu1Tc729k0gNxmAGQ8CrMxh/RKEi4lQEeWZnZfR+3qVog9nCDpmZTC?= =?us-ascii?Q?fLHOpvvX50sbJnsm/IqK9G7XAI7fFw4tMDS88GLtSbw5Kwz/K48KdjJml3/8?= =?us-ascii?Q?FDlA9xJce+QpPY22VxXYbB5ERW33WSGuBuREiCXU?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2009cb31-4253-4a87-24e6-08dd47c0c8ee X-MS-Exchange-CrossTenant-AuthSource: CY5PR12MB6405.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Feb 2025 21:45:48.8000 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 3CikyE1tJFIRTFNtGs+aB5UCIB4/kCIGSl5iWpWnJNY1YWkGdP6+dYzHQNYcNXvHG3xXRRnILjxgvwu6NfQlaw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB8126 On Fri, Feb 07, 2025 at 11:38:31AM -1000, Tejun Heo wrote: > Hello, > > On Fri, Feb 07, 2025 at 07:24:08AM +0100, Andrea Righi wrote: > > On Fri, Feb 07, 2025 at 12:13:36PM +0900, Changwoo Min wrote: > > > This patchset introduces a new event, SCX_EV_ENQ_SLICE_DFL, and updates > > > two scx schedulers -- scx_qmap and scx_central -- to print out the new > > > event. > > > > > > SCX_EV_ENQ_SLICE_DFL counts how many times the tasks' time slice is set > > > to the default value (SCX_SLICE_DFL) by the sched_ext core in the enqueue > > > and pick_next paths. > > > > > > Scheduling a task with SCX_SLICE_DFL unintentionally would be a source > > > of latency spikes because SCX_SLICE_DFL is relatively long (20 msec). > > > Thus, soaring the SCX_EV_ENQ_SLICE_DFL value would be a sign of BPF > > > scheduler bugs, causing latency spikes. > > > > Not directly related to this patch set, but as a general thought: would it > > be useful to introduce ops->slice_ms (in sched_ext_ops) to override > > SCX_SLICE_DFL? > > > > With that, schedulers that care about latency could set a smaller default > > time slice to prevent potential spikes caused by the implicit use of > > SCX_SLICE_DFL. > > > > Opinions? > > I'm not sure. BPF schedulers should be able to avoid getting the default > slice. Hopefully, with the added visibility, this should be easier now. I'm > not sure how much overriding the default value in ops helps in terms of > control. It's a very half-way measure. Instead, how about we add tracepoint > to scx_add_event() so that folks who want to get backtrace of specific > events can get them easily so that it's easier to debug where these counts > are coming from? Let's just make it easier to avoid these events. Yeah, that's a valid point, the implicit SCX_SLICE_DFL should be seen as a countermeasure for unhandled situations. Instead of fixing the countermeasure itself we should try to prevent it, if it proves to be problematic. And I like the idea of having a way to backtrace specific events. -Andrea