linux-kernel - Re: [PATCH v3 09/11] Input: alps - remove unlikely() from IS

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Date:   Sat, 31 Aug 2019 13:32:02 -0700
From:   Joe Perches <joe@...ches.com>
To:     Pali Rohár <pali.rohar@...il.com>,
        Denis Efremov <efremov@...ux.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-input@...r.kernel.org
Subject: Re: [PATCH v3 09/11] Input: alps - remove unlikely() from IS_ERR*()
 condition

On Sat, 2019-08-31 at 17:25 +0200, Pali Rohár wrote:
> On Thursday 29 August 2019 10:50:39 Dmitry Torokhov wrote:
> > On Thu, Aug 29, 2019 at 07:50:23PM +0300, Denis Efremov wrote:
> > > "unlikely(IS_ERR_OR_NULL(x))" is excessive. IS_ERR_OR_NULL() already uses
> > > unlikely() internally.
> > 
> > The keyword here is _internally_.
> > 
> > https://lore.kernel.org/lkml/20190821174857.GD76194@dtor-ws/
> > 
> > So please no.

I think it poor form not to simply restate your original
objection from 4 message levels below this link

https://lists.gt.net/linux/kernel/2269724

   Hm... I do not like this change. If I read code 
    
    if (unlikely(IS_ERR_OR_NULL(priv->dev3))) 
    
   then I know that it is really unlikely that condition will be truth and 
   so this is some case of error/exception or something that normally does 
   not happen too much. 
    
   But if I read code 
    
    if (IS_ERR_OR_NULL(priv->dev3)) 
    
   I know nothing about chance that this condition will be truth. Explicit 
   unlikely in previous example give me more information. 
    
I alslo think this argument is dubious as it also applies
to any IS_ERR and all the unlikely uses have been removed
from those.