Re: [patch] i386: use C code for current_thread_info()

[Chuck Ebbert]

In-Reply-To: <Pine.LNX.4.64.0606111225380.5498@xxxxxxxxxxx>

On Sun, 11 Jun 2006 12:33:10 -0700, Linus Torbalds wrote:

> On Sun, 11 Jun 2006, Chuck Ebbert wrote:
> >
> > Using C code for current_thread_info() lets the compiler optimize it.
> 
> Ok, me likee. I just worry that this might break some older gcc version. 
> Have you checked with gcc-3.2 or something?

I just tried gcc 3.3.3 and the kernel gets a little bigger but it boots
and runs OK. That's the oldest compiler I can find.

   text    data     bss     dec     hex filename
3593627  559864  342728 4496219  449b5b 2.6.17-rc6-32-post/vmlinux
3591371  559864  342728 4493963  44928b 2.6.17-rc6-32/vmlinux
  +2256

Looking at the generated code, it seems the compiler just makes dumb
choices and tends to recompute current_thread_info() in unlikely code
paths even when there is no register pressure.  4.0.2 makes better
choices.

-- 
Chuck

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