Messages in this thread | | | Date | Thu, 1 Mar 2018 08:15:44 -0700 | From | Keith Busch <> | Subject | Re: [PATCH V2] nvme-pci: assign separate irq vectors for adminq and ioq0 |
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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.
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