Subject: Re: get_current is __pure__, maybe __const__ even
From: Albert Cahalan <albert@users.sf.net>
To: Andi Kleen <ak@muc.de>
Cc: Albert Cahalan <albert@users.sourceforge.net>,
       linux-kernel mailing list <linux-kernel@vger.kernel.org>
In-Reply-To: <m3llfaya29.fsf@averell.firstfloor.org>
References: <2ER4z-46B-17@gated-at.bofh.it>
	 <m3llfaya29.fsf@averell.firstfloor.org>
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Date: 16 Sep 2004 09:43:01 -0400
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On Thu, 2004-09-16 at 02:58, Andi Kleen wrote:
> Albert Cahalan <albert@users.sf.net> writes:
> 
> > Andi Kleen writes:
> >
> >> Please CSE "current" manually. It generates
> >> much better code on some architectures
> >> because the compiler cannot do it for you.
> >
> > This looks fixable.
> 
> I tried it some years ago, but I ran into problems with the scheduler
> and some other code and dropped it.

Since then, have you changed:

a. the minimum required compiler version?
b. the clobbers on your switch_to asm?

If not, maybe you should.

> One problem is that gcc doesn't have a "drop all const/pure
> cache values" barrier. Without this I don't think it can be 
> safely implemented.

That's only if gcc can find some place to
hide state which will contaminate another task.
Where could that be? Remember, arm works.

Also, glibc works, with per-thread errno:

/* Function to get address of global `errno' variable.  */
extern int *__errno_location (void) __THROW __attribute__ ((__const__));

/* Function to get address of global `h_errno' variable.  */
extern int *__h_errno_location (void) __THROW __attribute__ ((__const__));


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