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Date: Sun, 11 Nov 2001 11:01:08 +1100
From: Anton Blanchard <anton@samba.org>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: "David S. Miller" <davem@redhat.com>, jakub@redhat.com, bcrl@redhat.com,
        torvalds@transmeta.com, alan@lxorguk.ukuu.org.uk, arjanv@redhat.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] take 2 of the tr-based current
Message-ID: <20011111110107.A4064@krispykreme>
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Hi,

> No. const == never changes.
> get_TR changes if a task calls schedule, and return on another cpu.

Yes, I found this exact problem on ppc64 where we would cache the
processor data area across a schedule(). What was interesting was that
__attribute__ ((pure)) was not enough to fix this.

static inline struct Paca *get_paca(void) __attribute__ ((pure));
static inline struct Paca *get_paca(void)
{
	struct Paca *rval;
	__asm__ ("mfspr %0,0x113" : "=r" (rval));
	return rval;
}

Alan Modra came to the rescue and found that gcc was optimising too much
and since the function did not touch any global variables, it would
upgrade the pure to const. This was on gcc 3.0.X.

Anton
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