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Re: [RFC] gcc feature request: Moving blocks into sections

From: Jason Baron <jbaron at akamai dot com>
To: Steven Rostedt <rostedt at goodmis dot org>
Cc: Linus Torvalds <torvalds at linux-foundation dot org>, LKML <linux-kernel at vger dot kernel dot org>, gcc <gcc at gcc dot gnu dot org>, Ingo Molnar <mingo at kernel dot org>, Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>, "H. Peter Anvin" <hpa at linux dot intel dot com>, Thomas Gleixner <tglx at linutronix dot de>, David Daney <ddaney dot cavm at gmail dot com>, Behan Webster <behanw at converseincode dot com>, Peter Zijlstra <peterz at infradead dot org>, Herbert Xu <herbert at gondor dot apana dot org dot au>
Date: Mon, 05 Aug 2013 16:06:48 -0400
Subject: Re: [RFC] gcc feature request: Moving blocks into sections
References: <1375721715 dot 22073 dot 80 dot camel at gandalf dot local dot home> <CA+55aFw_o=D-j_SRn=Y4LhHm-tEyuP1Je5ZHVTYxbVyLyDcLEg at mail dot gmail dot com> <1375725328 dot 22073 dot 101 dot camel at gandalf dot local dot home> <CA+55aFwRHpL-3YObZfw6NxxDxMqQbiwp0=NnpotGj2RHDNF3iw at mail dot gmail dot com> <1375727977 dot 22073 dot 112 dot camel at gandalf dot local dot home>

On 08/05/2013 02:39 PM, Steven Rostedt wrote:

On Mon, 2013-08-05 at 11:20 -0700, Linus Torvalds wrote:

Of course, it would be good to optimize static_key_false() itself -
right now those static key jumps are always five bytes, and while they
get nopped out, it would still be nice if there was some way to have
just a two-byte nop (turning into a short branch) *if* we can reach
another jump that way..For small functions that would be lovely. Oh
well.

I had patches that did exactly this:

  https://lkml.org/lkml/2012/3/8/461

But it got dropped for some reason. I don't remember why. Maybe because
of the complexity?

-- Steve


Hi Steve,

I recall testing your patches and the text size increased unexpectedly.I believe I correctly accounted for changes to the text size *outside*of branch points. If you do re-visit the series that is one thing I'dlike to double check/understand.


Thanks,

-Jason

References:
- [RFC] gcc feature request: Moving blocks into sections
  - From: Steven Rostedt
- Re: [RFC] gcc feature request: Moving blocks into sections
  - From: Linus Torvalds
- Re: [RFC] gcc feature request: Moving blocks into sections
  - From: Steven Rostedt
- Re: [RFC] gcc feature request: Moving blocks into sections
  - From: Linus Torvalds
- Re: [RFC] gcc feature request: Moving blocks into sections
  - From: Steven Rostedt

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