linux-kernel - Re: [PATCH 1/1] Trivial: devtmpfsd: Setting task running/interruptible states

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Date:	Thu, 22 Sep 2011 08:55:12 +0530
From:	"kautuk.c @samsung.com" <consul.kautuk@...il.com>
To:	Greg KH <gregkh@...e.de>
Cc:	Jiri Kosina <trivial@...nel.org>, jkosina@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Trivial: devtmpfsd: Setting task running/interruptible
 states

On Thu, Sep 22, 2011 at 2:40 AM, Greg KH <gregkh@...e.de> wrote:
> On Wed, Sep 21, 2011 at 09:54:01PM +0530, kautuk.c @samsung.com wrote:
>> Hi Greg,
>>
>> On Wed, Sep 21, 2011 at 9:24 PM, Greg KH <gregkh@...e.de> wrote:
>> > On Wed, Sep 21, 2011 at 09:09:33PM +0530, Kautuk Consul wrote:
>> >> This trivial patch makes the following changes in devtmpfsd() :
>> >
>> > This is not the definition of "trivial" in that you are changing the
>> > logic of the code, not just doing spelling changes.
>>
>> Well, I didn't really change the performance/functionality so I called
>> it trivial.
>
> You changed the code logic,

Hmm. Not the code logic of devtmpfsd as such but of the loop involved.

> which is not trivial at all in this area.

Ok.
If you want, maybe I could send another patch for this without marking
it "trivial".

>
> And actually unneeded from what I can tell, right?

Well, there *are* 2 overheads.
As I mentioned, the overheads which I tried to remove by this patch is an extra
memory barrier as well as setting of the task state to TASK_RUNNING.
Of course, they are very minimal and that's why I called this change "trivial".

>
>> >
>> >> - Set the state to TASK_INTERRUPTIBLE using __set_current_state
>> >>   instead of set_current_state as the spin_unlock is an implicit
>> >>   memory barrier.
>> >
>> > Why?  What is this hurting with the original code?
>>
>> Nothing really hurting, that's why I called this patch trivial.
>> There is an extra memory barrier we have to go through by way of
>> set_current_state, which is mb().
>> That would lead to more overhead on the parallel pipelines of the processor
>> as they will have to cease being parallel for instructions before and after
>> the memory barrier despite the fact that the spin_unlock already covers this.
>> We can do without this because as per the Documentation/memory-barriers.txt,
>> atomic operations and unlocks give reliable ordering to instructions.
>
> But the current code is correct, and not hurting anything, and it's not
> on a "fast path" at all, so I'd prefer to keep it as-is and not change
> it for the sake of changing it, so I'm not going to accept this patch,
> sorry.

Ok.
However, I see many changes going in which are purely cosmetic like
restructuring or clean-up of a function, etc.
So this is a category of change that lies (in importance) between a
cosmetic/trivial
change and a minor logic change.
Since this patch is still technically correct, do you mean to say that
this cannot even
be looked as some sort of a "technical" cleanup ?

Also, I see you did not include my comment about the removal of the setting of
TASK_RUNNING. Do you at least accept that ?
If that is so, maybe you could accept the first patch I sent.

Anyway, thanks for the info.

>
> greg k-h
>
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