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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?QuP35vQOE52nMUuAWD/IpFCBw+3NhbPJWSZ8ieX9lc8YBDNz9V98i+fzTPvI?= =?us-ascii?Q?1H2nCtyoDXpx3xmRWC+OgE8Uh4FUZUOFw4xInVtFlYA7M0QZUREPhnE3if5/?= =?us-ascii?Q?+fBIEFGjtm23BCxsZVRQUJFJaE9bNgkWaruxdoNsQsONgpAAvMGzBeZRHmJi?= =?us-ascii?Q?sHlPaTAS3n+TgUU8tXZf8TZH5ZSHx/6k32bvLFEY+d1ITEY3IuDvZm0+ttDv?= =?us-ascii?Q?efOmpc7GHpcvtOR+3mrGD0caIFwgkY86NlzEXMaSDFf3y4ZiegsahliOqIWZ?= =?us-ascii?Q?BT5IWHf2g7M+qD3T4M1WTBECQUB/Cgf7H78u7q3g5A0kS+LsfH+4KyynW9hu?= =?us-ascii?Q?Jb2h9FxVXq77ocKoBL17mvZoac4/n+QtMJ9mM2dVsmfVB5w1xmgBvgyRUUNg?= =?us-ascii?Q?n4qAzXpiCBjFoW3Weuhel78nDeTR6uMBXobf0E9K31sg+30MKUdVpdbQrmAV?= =?us-ascii?Q?Nl8YRKon4hrTAtnHLLg1rIHLB0pDhxmeS3ab3fFB6qnWZaGfFuczLlHM4yd7?= =?us-ascii?Q?K5XIESPHNzd/U2e8qDhzQ7SfhD3ElScXUzxlUFNDrPui7mJT/hBf46dRaCik?= =?us-ascii?Q?sgMunLplUzJqt+sjCEzLSKOvTpaE2Xuf9CIMf646cXFVCZSdd/ldnkGkysnP?= =?us-ascii?Q?X/0pY18gbCty854QNl/RI9YaHAFt6fW8WiN7KxwA71FsnQr43N6lLrwgxYGA?= =?us-ascii?Q?qFa6IViq60fGErIZmvivRHml+Yxdz9SgOwR7kRZoBaY/IY7qvA9hUgarUs77?= =?us-ascii?Q?KiXADNCdL3RzBiK/T1xBPOiRYN7UEyQmd+FpFw3YSe1yJ6cnRMJeaYWfHfay?= =?us-ascii?Q?VfxBIkmDmeUlZBn1uEGXKNdHGoC41opnxrD1tLuqCsQOnXc2ENBLNWtD1zPK?= =?us-ascii?Q?Hk1BlQTkRGloVVJ3zJh6C1IaKndRLY9HX4s+PpqjMB/AFlYVLpl/dNMYRNHv?= =?us-ascii?Q?kWaGfKMvQGPc9G6/dqPB8bMUcAo+XH08OCK1PngJUUZZzfBzEMVHG76iwc+A?= =?us-ascii?Q?1nA08buy73ZXhIAYk4k23tkT7Bb1lXgC78LSE/5XmZXM0CWjw7gsNoD4fDkn?= =?us-ascii?Q?MSwJcPG9OMAqwlD+sUV8wb53TJmwAlxdLBxkq119IotC0paMDiv/+iJuwWEn?= =?us-ascii?Q?S37EHM/ufXPqObwC8qFqCeQRpC/vNrAzdOQsHACc8QQT+j/QJpeQvr1E5Ni4?= =?us-ascii?Q?0lB8ZGMtsv/OwCZvL3Y1kufTQbxZYwmMq/7w4p60xrRRzXr/XjCyciP6g4N+?= =?us-ascii?Q?dN0/dWAcAek7bSoD/Jnym1dNvVXOsd6Zt4CxV7jyKkflwlT2s3cQ0Axv2gcj?= =?us-ascii?Q?VbsgbGt1WgqbnCnQ9/nk1UVjd7g8D2Ohx7Y3DjcSOelhWcfBD0RtYH8Y61xD?= =?us-ascii?Q?IJAHrKTT32FHyWO0cazarYIFc4+kF0Hcqddjw99Rzu0UPoKC7TZjEdLh9+J+?= =?us-ascii?Q?ZPlibNtFV7JfPf0mfqREj2uq6g2R96t8zZAjn356ScAz8FJ1psLseSeOsS5g?= =?us-ascii?Q?spJ9TbnVYD16ZZycAK5PeJGRLKvjQZl6/1dHB9SKsM6romMcHTqefl8dcHnR?= =?us-ascii?Q?9ki7aTIjNB09RRmoSsm11v+JduvWzM3ZgyQvFFYv?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 55f3547b-13e0-4026-2e60-08dd2b5ee83a X-MS-Exchange-CrossTenant-AuthSource: CY5PR12MB6405.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Jan 2025 18:54:38.1018 (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: 7AwR+FaT8+mv7xcF5r4Zzofpge1eXb1lJer7fJj3Yy2WlSDUGf75RI8umtTgR+iScSS8pExCirS08ws1r6iW/Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB8243 Hi Changwoo, On Mon, Dec 30, 2024 at 06:56:19PM +0900, Changwoo Min wrote: > Many BPF schedulers (such as scx_central, scx_lavd, scx_rusty, scx_bpfland, > and scx_flash) frequently call bpf_ktime_get_ns() for tracking tasks' runtime > properties. If supported, bpf_ktime_get_ns() eventually reads a hardware > timestamp counter (TSC). However, reading a hardware TSC is not > performant in some hardware platforms, degrading IPC. > > This patchset addresses the performance problem of reading hardware TSC > by leveraging the rq clock in the scheduler core, introducing a > scx_bpf_now() function for BPF schedulers. Whenever the rq clock > is fresh and valid, scx_bpf_now() provides the rq clock, which is > already updated by the scheduler core (update_rq_clock), so it can reduce > reading the hardware TSC. > > When the rq lock is released (rq_unpin_lock), the rq clock is invalidated, > so a subsequent scx_bpf_now() call gets the fresh sched_clock for the caller. > > In addition, scx_bpf_now() guarantees the clock is monotonically > non-decreasing for the same CPU, so the clock cannot go backward > in the same CPU. > > Using scx_bpf_now() reduces the number of reading hardware TSC > by 50-80% (76% for scx_lavd, 82% for scx_bpfland, and 51% for scx_rusty) > for the following benchmark: > > perf bench -f simple sched messaging -t -g 20 -l 6000 Looks good to me, I also tested it and I have nothing to report, therefore: Acked-by: Andrea Righi Thanks, -Andrea