Hi Morten and Hemant, YIELD is a NOP on non-SMT CPUs, such as Neoverse.
WFE is universally available on AArch64, but it comes with a caveat: the CPU can remain in a low-power state indefinitely unless an event is triggered. That event can be generated explicitly via SEV/SEVL by a different CPU, or implicitly through address monitoring (LDAXR).
WFET is the safer variant because it includes a timeout, so explicit or implicit event-register manipulation is not required.
--wathsala On 6/12/26 01:11, Hemant Agrawal wrote:
Hi Morten, On Cortex‑A72 (ARMv8), the only architectural primitives available are YIELD, WFE, and WFI: YIELD is the only deterministic, low-overhead option (pure CPU relax, no entry into low-power state) WFE can be used as a low-power idle hint, but it is event-driven and not time-based (it may return immediately) WFI depends on interrupt wakeup and is therefore not suitable for tight latency loops For ~1 µs latency targets, the practical approach is a hybrid strategy: Short waits → spin using YIELD Slightly longer waits → opportunistically use WFE for power reduction A simple implementation could look like (not tested): static inline void rte_armv8_pause(unsigned int iters) { if (iters < 64) { for (unsigned int i = 0; i < iters; i++) asm volatile("yield"); } else { asm volatile("sevl"); asm volatile("wfe"); } } @Wathsala Vithanage — would appreciate your thoughts, especially if there are any micro-architectural nuances we should consider. Regards, Hemant-----Original Message----- From: Morten Brørup <[email protected]> Sent: 03 June 2026 17:26 To: Wathsala Vithanage <[email protected]>; Hemant Agrawal <[email protected]>; Sachin Saxena (OSS) <[email protected]> Cc: [email protected]; Maxime Leroy <[email protected]> Subject: ARM v8 rte_power_pause Importance: High Hi Wathsala, Hemant and Sachin, Over at the Grout project, we are discussing power management in the context of 100 Gbit/s latency deadlines [1]. rte_power_pause() is not implemented for ARM v8 / Cortex-A72. Syscalls such as nanosleep() have too much overhead, and cannot be used. Any suggestions for a power-reducing method to make a CPU core "sleep" (i.e. do nothing) for durations in the order of 1 microsecond? [1]: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithu b.com%2FDPDK%2Fgrout%2Fpull%2F624%23issuecomment- 4602036364&data=05%7C02%7Chemant.agrawal%40nxp.com%7Cdbff5f2e 8db1406f0c4008dec1671791%7C686ea1d3bc2b4c6fa92cd99c5c301635%7 C0%7C0%7C639160845728472826%7CUnknown%7CTWFpbGZsb3d8eyJFb XB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTW FpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=DRpJWjm2yaF3Cnhk0b bFFhmGbKRweOOiWdsWco2NbX0%3D&reserved=0 -Morten
