NVME io_poll with kernel 5.x

NVME io_poll with kernel 5.x

[vrd]

Hi,

Since commit a4668d9ba ("nvme: default to 0 poll queues") [1], the nvme driver needs to be explicitly configured with poll_queues > 0 to allow enabling io_poll.

However, prior to poll queues separation in 4b04cc6a8 ("nvme: add separate poll queue map") [2], io_poll was enabled by default on nvme block devices. How does this work on older kernels, without dedicated poll queues?

The commit [1] says:

> We need a better way of configuring this, and given that polling is
> (still) a bit niche, let's default to using 0 poll queues.

Are there any plans / work needed for nvme to provide > 0 poll_queues by default?


[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=a4668d9ba
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=4b04cc6a8

Thanks,
Varad



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Re: NVME io_poll with kernel 5.x

[Christoph Hellwig]

On Wed, Jul 22, 2020 at 03:05:50PM +0200, vrd@amazon.com wrote:
> Hi,
> 
> Since commit a4668d9ba ("nvme: default to 0 poll queues") [1], the nvme driver needs to be explicitly configured with poll_queues > 0 to allow enabling io_poll.
> 
> However, prior to poll queues separation in 4b04cc6a8 ("nvme: add separate poll queue map") [2], io_poll was enabled by default on nvme block devices. How does this work on older kernels, without dedicated poll queues?
> 
> The commit [1] says:
> 
> > We need a better way of configuring this, and given that polling is
> > (still) a bit niche, let's default to using 0 poll queues.
> 
> Are there any plans / work needed for nvme to provide > 0 poll_queues by default?

Not that I know of.  If you have a good suggestion you're welcome to
propose something, though.

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