Hi Keith Thanks for your kindly directive and precious time for this.
On 03/01/2018 11:15 PM, Keith Busch wrote: > 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. Yes, indeed, sorry for my bad description. >> 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. > Yes, indeed Sincerely Jianchao