netdev - Re: [PATCH] net: remove redundant checking for sock timer state

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Message-ID: <1359700003.30177.32.camel@edumazet-glaptop>
Date:	Thu, 31 Jan 2013 22:26:43 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	ying.xue@...driver.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: remove redundant checking for sock timer state

On Fri, 2013-02-01 at 01:09 -0500, David Miller wrote:
> From: Ying Xue <ying.xue@...driver.com>
> Date: Fri, 1 Feb 2013 13:53:00 +0800
> 
> > It's unnecessary to check whether the sock timer to be stopped is
> > pending or not in sk_stop_timer() as del_timer() will do the same
> > thing later.
> > 
> > Signed-off-by: Ying Xue <ying.xue@...driver.com>
> 
> Did it even occur to you that when this code was written, this
> "redundant" testing was also redundant, but that it might have been
> done on purpose?
> 
> If you are going to change this code, you must understand why it was
> written this way, because that is the only context in which you will
> be able to justify removing the test.
> 

I had the same reaction but maybe its not anymore a valid thing.

Before commit 55c888d6d ([PATCH] timers fixes/improvements) there was
indeed a significant cost calling del_timer() because of unconditional
spinlock acquisition.

But nowadays del_timer() doesn't blindly lock the spinlock.

So I guess we could change all occurrences of :

if (timer_pending(X))
    del_timer(X);

It would save some bytes of code.

But please Ying, do a complete patch for net tree, don't send 30
patches.



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