Re: Why is MEGASAS_SAS_QD set to 256?

[Yu Kuai]

在 2022/11/26 14:08, Yu Kuai 写道:
> Hi, Ming
>
> 在 2022/11/26 10:18, Ming Lei 写道:
> > If you want aggressive merge on sequential IO workload, the queue 
> > depth need
> > to be a bit less, then more requests can be staggered into scheduler 
> > queue,
> > and merge chance is increased.
>
> But if nr_requests >= queue_depth, it seems to me elevator will have no
> effect, no request can be merged or sorted by scheduler, right?
Sorry that should be nr_requests <= queue_depth.

> > If you want good perf on random IO perf, the queue depth needs to
> > be deep enough to have enough parallelism for saturating SSD internal.
> >
> > But we don't recognize sequential/random IO pattern, and usually fixed
> > queue depth is used.
>
> Is it possible to use none elevator and set large queue_depth if nvme is
> used in this case?
>
> Thansk,
> Kuai
> > Thanks,
> > Ming
> >
> > .
>
> .