On 3/3/20 11:17 PM, Hannes Reinecke wrote:
there had been quite some discussion around completion polling and the fact that for high-performance devices it might be a performance benefit [1][2]. And during discussion with other people (hello tglx) the reaction always had been "Can't you do NAPI?" So the question is: Can we? IE is it possible to have a generic framework for handling polled completiona and interrupt completions, shifting between them depending on the load? My idea is to have a sequence like completion polling -> interrupt handling -> threaded irq/polling IE invoke completion polling directly from the submission path, enable interrupts to handle completions from the interrupt handler, and finally shift to completion polling again if too many completions are present. Clearly this approach involves quite some tunables (like how many completions before enabling polling from interrupt context, how long to wait for completions before enabling interrupts etc), but I thing it would be worthwhile having this as a generic framework as then one could start experimenting with the various tunables to see which works best for the individual hardware. And it would lift the burden from the hardware vendors to implement a similar mechanism on their own.
To me the above sounds like a description of the lib/irq_poll mechanism? From the top of lib/irq_poll.c:
/* * Functions related to interrupt-poll handling in the block layer. This * is similar to NAPI for network devices. */ Anyway, I'm interested in participating in the discussion of this topic. Bart.
