Re: [PATCH] Input: alps: Drop unlikely before IS_ERR(_OR_NULL)
From: Dmitry Torokhov
Date: Tue Jun 11 2019 - 21:03:52 EST
On Wed, Jun 05, 2019 at 07:28:53PM -0700, Joe Perches wrote:
> On Thu, 2019-06-06 at 09:08 +0800, Kefeng Wang wrote:
> > On 2019/6/5 22:42, Pali Rohár wrote:
> > > On Wednesday 05 June 2019 22:24:28 Kefeng Wang wrote:
> > > > IS_ERR(_OR_NULL) already contain an 'unlikely' compiler flag,
> > > > so no need to do that again from its callers. Drop it.
> > > Hi! I already reviewed this patch and rejected it, see:
> > > https://patchwork.kernel.org/patch/10817475/
> > OK, please ignore it.
> I think the stated reason of better readability isn't
> particularly sensible as the object code produced is
> actually slightly larger.
> x86-64 defconfig (gcc 8.3.0)
> $ size drivers/input/mouse/alps.o*
> text data bss dec hex filename
> 29416 56 0 29472 7320 drivers/input/mouse/alps.o.new
> 29432 56 0 29488 7330 drivers/input/mouse/alps.o.old
If gcc produces worse code for double unlikely, you should probably
report it to gcc folks, no? Or double unlikely turns into likely?
> Also if this unlikely is _really_ useful, perhaps the
> !IS_ERR immediately after could also use likely as the
> test seems only done for an OOM condition.
No, once you take the IS_ERR_OR_NULL(priv->dev3) == true branch it stops
being hot path and additional annotations are completely unneeded.
And if we failed to create and register priv->dev3 device - that's an
error and system is degraded. Can't do much here.