On Mon, 1 Jul 2019 00:21:11 +0800 Gavin Hu <gavin...@arm.com> wrote:
> DPDK has multiple use cases where the core repeatedly polls a location in > memory. This polling results in many cache and memory transactions. > > Arm architecture provides WFE (Wait For Event) instruction, which allows > the cpu core to enter a low power state until woken up by the update to the > memory location being polled. Thus reducing the cache and memory > transactions. > > x86 has the PAUSE hint instruction to reduce such overhead. > > The rte_wait_until_equal_xxx APIs abstract the functionality of 'polling > for a memory location to become equal to a given value'. > > For non-Arm platforms, these APIs are just wrappers around do-while loop > with rte_pause, so there are no performance differences. > > For Arm platforms, use of WFE can be configured using CONFIG_RTE_USE_WFE > option. It is disabled by default. > > Currently, use of WFE is supported only for aarch64 platforms. armv7 > platforms do support the WFE instruction, but they require explicit wake up > events(sev) and are less performannt. > > Testing shows that, performance varies across different platforms, with > some showing degradation. > > CONFIG_RTE_USE_WFE should be enabled depending on the performance on the > target platforms. How does this work if process is preempted?
