ARM v8 rte_power_pause

[Hemant Agrawal]

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 <mb at smartsharesystems.com>
> Sent: 03 June 2026 17:26
> To: Wathsala Vithanage <wathsala.vithanage at arm.com>; Hemant Agrawal
> <hemant.agrawal at nxp.com>; Sachin Saxena (OSS)
> <sachin.saxena at oss.nxp.com>
> Cc: dev at dpdk.org; Maxime Leroy <maxime at leroys.fr>
> 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