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From: Andrew Morton <akpm@linux-foundation.org>
To: Daniel Santos <daniel.santos@pobox.com>
Cc: Daniel Santos <danielfsantos@att.net>,
	Michel Lespinasse <walken@google.com>,
	riel@redhat.com, peterz@infradead.org, aarcange@redhat.com,
	dwmw2@infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, torvalds@linux-foundation.org
Subject: Re: [PATCH v3 2/9] rbtree: add __rb_change_child() helper function
Date: Wed, 26 Sep 2012 15:43:45 -0700	[thread overview]
Message-ID: <20120926154345.52cb9f33.akpm@linux-foundation.org> (raw)
In-Reply-To: <506382E3.3020102@att.net>

On Wed, 26 Sep 2012 17:34:11 -0500
Daniel Santos <danielfsantos@att.net> wrote:

> Sorry to resurrect the dead here, but I'm playing catch-up and this
> looks important.
> 
> On 08/20/2012 05:17 PM, Andrew Morton wrote:
> > I'm inclined to agree with Peter here - "inline" is now a vague,
> > pathetic and useless thing.  The problem is that the reader just
> > doesn't *know* whether or not the writer really wanted it to be
> > inlined.
> >
> > If we have carefully made a decision to inline a function, we should
> > (now) use __always_inline.
> Are we all aware here that __always_inline (a.k.a.
> "__attribute__((always_inline))") just means "inline even when not
> optimizing"?  This appears to be a very common misunderstanding (unless
> the gcc docs are wrong, see
> http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#index-g_t_0040code_007bflatten_007d-function-attribute-2512).
> 
> If you want to *force* gcc to inline a function (when inlining is
> enabled), you can currently only do it from the calling function by
> adding the |flatten attribute to it, which I have proposed adding here:
> https://lkml.org/lkml/2012/9/25/643.
> 
> Thus, all of the __always_inline markings we have in the kernel only
> affect unoptimized builds (and maybe -O1?).  If we need this feature
> (and I think it would be darned handy!) we'll have to work on gcc to get it.

When I replace the four __always_inline's in fs/namei.c with "inline",
namei.o's .text shrinks 2kbytes (gcc-4.4.4), so __always_inline does
allear to be doing what we think it does?



WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Daniel Santos <daniel.santos@pobox.com>
Cc: Daniel Santos <danielfsantos@att.net>,
	Michel Lespinasse <walken@google.com>,
	riel@redhat.com, peterz@infradead.org, aarcange@redhat.com,
	dwmw2@infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, torvalds@linux-foundation.org
Subject: Re: [PATCH v3 2/9] rbtree: add __rb_change_child() helper function
Date: Wed, 26 Sep 2012 15:43:45 -0700	[thread overview]
Message-ID: <20120926154345.52cb9f33.akpm@linux-foundation.org> (raw)
In-Reply-To: <506382E3.3020102@att.net>

On Wed, 26 Sep 2012 17:34:11 -0500
Daniel Santos <danielfsantos@att.net> wrote:

> Sorry to resurrect the dead here, but I'm playing catch-up and this
> looks important.
> 
> On 08/20/2012 05:17 PM, Andrew Morton wrote:
> > I'm inclined to agree with Peter here - "inline" is now a vague,
> > pathetic and useless thing.  The problem is that the reader just
> > doesn't *know* whether or not the writer really wanted it to be
> > inlined.
> >
> > If we have carefully made a decision to inline a function, we should
> > (now) use __always_inline.
> Are we all aware here that __always_inline (a.k.a.
> "__attribute__((always_inline))") just means "inline even when not
> optimizing"?  This appears to be a very common misunderstanding (unless
> the gcc docs are wrong, see
> http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#index-g_t_0040code_007bflatten_007d-function-attribute-2512).
> 
> If you want to *force* gcc to inline a function (when inlining is
> enabled), you can currently only do it from the calling function by
> adding the |flatten attribute to it, which I have proposed adding here:
> https://lkml.org/lkml/2012/9/25/643.
> 
> Thus, all of the __always_inline markings we have in the kernel only
> affect unoptimized builds (and maybe -O1?).  If we need this feature
> (and I think it would be darned handy!) we'll have to work on gcc to get it.

When I replace the four __always_inline's in fs/namei.c with "inline",
namei.o's .text shrinks 2kbytes (gcc-4.4.4), so __always_inline does
allear to be doing what we think it does?


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  reply	other threads:[~2012-09-26 22:43 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-20 22:05 [PATCH v3 0/9] faster augmented rbtree interface Michel Lespinasse
2012-08-20 22:05 ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 1/9] rbtree test: fix sparse warning about 64-bit constant Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 2/9] rbtree: add __rb_change_child() helper function Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:17   ` Andrew Morton
2012-08-20 22:17     ` Andrew Morton
2012-08-23 12:05     ` Jan Engelhardt
2012-08-23 12:05       ` Jan Engelhardt
2012-08-23 13:08       ` David Woodhouse
2012-09-26 22:34     ` Daniel Santos
2012-09-26 22:34       ` Daniel Santos
2012-09-26 22:43       ` Andrew Morton [this message]
2012-09-26 22:43         ` Andrew Morton
2012-08-20 22:05 ` [PATCH v3 3/9] rbtree: place easiest case first in rb_erase() Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:28   ` Andrew Morton
2012-08-20 22:28     ` Andrew Morton
2012-08-20 22:05 ` [PATCH v3 4/9] rbtree: handle 1-child recoloring in rb_erase() instead of rb_erase_color() Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 5/9] rbtree: low level optimizations in rb_erase() Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 6/9] rbtree: augmented rbtree test Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 7/9] rbtree: faster augmented rbtree manipulation Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 8/9] rbtree: remove prior augmented rbtree implementation Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse
2012-08-20 22:05 ` [PATCH v3 9/9] rbtree: add RB_DECLARE_CALLBACKS() macro Michel Lespinasse
2012-08-20 22:05   ` Michel Lespinasse

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