Re: [PATCH] Improve accuracy of rate= option

[Jens Axboe <axboe@kernel.dk>]

On 2011-11-09 02:10, Steven Lang wrote:
> I noticed that the rate= option is not terribly precise in some cases.
>  It gets worse the higher the selected rate.  For example:
> $ fio -name=load -size=100g -ioengine=null -runtime=10 -rate=30m
> One would expect that to read 300MB (307200KB) at close to 30MB/s
> (30720KB/s).  However it writes 315024KB at 31499KB/s.  Further
> experimentation shows that even higher rates can show bigger
> discrepancies.  At the extreme end...
> $ fio -name=load -size=100g -ioengine=null -runtime=10 -rate=500m
> One would expect this to write 5000MB at a rate of 500MB/s
> (512000KB/s).  However it writes close to double that (9536.8MB) at a
> rate of over 953MB/s.  At a rate of 1GB/s and higher, the rate
> limiting is effectively ignored.
> 
> This patch improves the accuracy of the rate= option across the whole
> range of rates, at the cost of being very slightly more
> computationally expensive.

Thanks Steven, another great patch. Applied.

I'm still mulling over the option patch. It'd be great if one could do:

$ fio --cmdhelp=ioengine=libaio

to display these private options. And it's a bit confusing on the global
vs private engine options, but in reality it _probably_ wont bite
anyone.

Anyway, I fiddle with it a bit and let you know.

-- 
Jens Axboe