linux-kernel - Re: [RFC PATCH 1/5] cfq-iosched: adapt slice to number of processes doing I/O

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Date:	Tue, 20 Oct 2009 20:11:19 +0200
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [RFC PATCH 1/5] cfq-iosched: adapt slice to number of processes 
	doing I/O

On Tue, Oct 20, 2009 at 3:17 PM, Jens Axboe <jens.axboe@...cle.com> wrote:
> I do, personally it doesn't read anywhere near as naturally as a simple
> 'if'. And when you start doing x = a ? b : c ? d : e; I almost reach for
> the nearest expletive :-)
In this case, formatting it on multiple lines could help:
 a ? b :
   c ? d :
   e;
>
> And adding a local scope with {} and having 3-4 broken lines of
> multiplications, divisions (etc) inside max()/min() calls doesn't add to
> the readability in any positive way...

Ok, but min and max hide a lot of complexity for the corner cases.
Espressing those with plain ifs would be really a tough task.

>
>> To me, it seems a good way to achieve a different readability goal,
>> i.e. define the value of a variable in a single place, instead of
>> scattering it around on multiple lines.
>
> I prefer putting it elsewhere instead. So instead of doing:
>
>        foo_type bar = x(y) == BAZ ? a : b;
>
> you have
>
> get_foo_type(y)
> {
>        if (x(y) == BAZ)
>                return a;
>
>        return b;
> }
>
>        foo_type bar = get_foo_type(y);
>
> which is a lot more readable to me. Especially since you have to do the
> get_foo_type() operation in a lot of places.

Sounds good. I'll do in this way in next version.

>
>> It's not important for the patches per se, but I found odd (and it
>> caused me some headache while debugging) that in cfq_add_rq_rb the
>> fifo was still empty.
>> In the new form, the rq will be complete when added, while in the
>> previous, it still had some empty fields.
>
> Then keep it like it is, or do it as a separate patch. When you include
> it in a functionally changing patch like this, I'm assuming there must
> be a reason for that. And when it seems like there isn't, you wonder
> what is up.

I'm moving it in the preparation patch, that is not changing
functionality. There,. it makes more sense.

I'm going to send the revised series soon.

Corrado
>
> --
> Jens Axboe
>
>



-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@...il.com
PhD - Department of Computer Science - University of Pisa, Italy
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