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

[Ingo Molnar]

* Suparna Bhattacharya <suparna@xxxxxxxxxx> 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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/