Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3)

Ingo Molnar
2007-02-26T14:25:05Z

* Suparna Bhattacharya <suparna@in.ibm.com> wrote:

> > syslet still on top. Measuring O_DIRECT reads (of 4kb size) on ramfs
> > with 100 processes each with a depth of 200, reading a per-process
> > private file of 10mb (need to fit in my ram...) 10 times each. IOW,
> > doing 10,000MiB of IO in total:
>
> But, why ramfs ? Don't we want to exercise the case where O_DIRECT
> actually blocks ? Or am I missing something here ?

ramfs is just the easiest way to measure the pure CPU overhead of a
workload without real IO delays (and resulting idle time) getting in the
way. It's certainly not the same thing, but still it's pretty useful
most of the time. I used a different method, loopback block device, and
got similar results. [ Real IO shows similar results as well, but is a
lot more noisy and hence harder to interpret (and thus easier to get
wrong). ]

Ingo