Re: use of rwmixread option

[Jens Axboe <axboe@kernel.dk>]

On Thu, Jan 31 2013, Carl Zwanzig wrote:
> Hi,
> 
> Am I correct that rwmixread/rwmixwrite are completely ignored unless
> readwrite=rw or =randrw? Experiments suggest yes but I can't find
> where this is handled in the code. (The HowTo file is silent on this.)

That is correct, see io_u.c:get_rw_ddir(). The mix is only used if the
data direciton is read-write. For pure read, always reads, for pure
writes, always writes.

> *Is there a description somewhere on how options are processed?
> Tracking the option definition in options.c to its use has eluded me.

So the options.c bits only ensure that the options are set. That is
td->o.rwmix[]. The options ensure that mixread + mixwrite == 100%. The
actual handling is in the function mentioned above, plus it interacts
with an IO issue counter. Essentially the mix is IOPS based, with
randomness for direction chosen.

-- 
Jens Axboe