On Fri, Nov 30, 2018 at 12:00:13AM -0800, Christoph Hellwig wrote:
> On Thu, Nov 29, 2018 at 01:19:14PM -0700, Keith Busch wrote:
> > On Thu, Nov 29, 2018 at 08:12:58PM +0100, Christoph Hellwig wrote:
> > > +enum hctx_type {
> > > + HCTX_TYPE_DEFAULT, /* all I/O not otherwise accounted for */
> > > + HCTX_TYPE_READ, /* just for READ I/O */
> > > + HCTX_TYPE_POLL, /* polled I/O of any kind */
> > > +
> > > + HCTX_MAX_TYPES,
> > > };
> >
> > Well, there goes my plan to use this with Weighted-Round-Robin NVMe IO
> > queues!
>
> Wo between what do you even want to round robin? If it is between
> reads and writes that's easy. If we want priority reads or writes
> (separate from polling) that's also still fairly easily.
I was considering the IOPRIO_PRIO_CLASS. There are four of them, which
may roughly correspond to the four NVMe IO queues weights. Maybe even
through HIPRI flagged IOs with the RT class.
> Btw, one thing I wanted to try once I get hold of the right hardware
> is to mark the poll queues as priority queues and see if that makes
> any differents in poll IOPS/latency.
I doubt it will make much difference in IOPS, but should improve latency
on hipri IOs at the expense of normal IO since hipri will be fetched
ahead during command arbitrarion.
