Re: Why is MEGASAS_SAS_QD set to 256?

[Yu Kuai]

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?
> 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
>
> .