On Thu, Mar 01, 2018 at 06:05:53PM +0800, jianchao.wang wrote: > When the adminq is free, ioq0 irq completion path has to invoke nvme_irq > twice, one for itself, > one for adminq completion irq action.
Let's be a little more careful on the terminology when referring to spec defined features: there is no such thing as "ioq0". The IO queues start at 1. The admin queue is the '0' index queue. > We are trying to save every cpu cycle across the nvme host path, why we waste > nvme_irq cycles here. > If we have enough vectors, we could allocate another irq vector for adminq to > avoid this. Please understand the _overwhelming_ majority of time spent for IRQ handling is the context switches. There's a reason you're not able to measure a perf difference between IOQ1 and IOQ2: the number of CPU cycles to chain a second action is negligible.
