Re: Linux I/O tuning: CFQ vs. deadline

Greg Smith wrote:
> Recently I've made a number of unsubstantiated claims that the deadline
> scheduler on Linux does bad things compared to CFQ when running
> real-world mixed I/O database tests. Unfortunately every time I do one
> of these I end up unable to release the results due to client
> confidentiality issues. However, I do keep an eye out for people who
> run into the same issues in public benchmarks, and I just found one:
> http://insights.oetiker.ch/linux/fsopbench/

That is interesting; particularly since I have made one quite different
experience in which deadline outperformed CFQ by a factor of approximately 4.

So I tried to look for differences, and I found two possible places:
- My test case was read-only, our production system is read-mostly.
- We did not have a RAID array, but a SAN box (with RAID inside).

The "noop" scheduler performed about as well as "deadline".
I wonder if the two differences above could explain the different
result.

Yours,
Laurenz Albe