Re: [LSF/MM TOPIC][LSF/MM ATTEND] NAPI polling for block drivers

Johannes Thumshirn
2017-01-11T16:14:29Z

On Wed, Jan 11, 2017 at 04:08:31PM +0000, Bart Van Assche wrote:

[...]

> A typical Ethernet network adapter delays the generation of an interrupt
> after it has received a packet. A typical block device or HBA does not delay
> the generation of an interrupt that reports an I/O completion. I think that
> is why polling is more effective for network adapters than for block
> devices. I'm not sure whether it is possible to achieve benefits similar to
> NAPI for block devices without implementing interrupt coalescing in the
> block device firmware. Note: for block device implementations that use the
> RDMA API, the RDMA API supports interrupt coalescing (see also
> ib_modify_cq()).

Well you can always turn off IRQ generation in the HBA just before scheuduling
the poll handler and re-enable it after you've exhausted your budget or used
too much time, can't you?

I'll do some prototyping and tests tomorrow so we have some more ground for
discussion.

Byte,
Johannes
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