Re: Why is MEGASAS_SAS_QD set to 256?

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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

.


.





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