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Re: jiffies_64 vs. jiffies

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: jiffies_64 vs. jiffies
From: Paul Mackerras <paulus@samba.org>
Date: Fri, 3 Mar 2006 15:06:16 +1100
Cc: linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, akpm@osdl.org
In-reply-to: <20060301.144442.118975101.nemoto@toshiba-tops.co.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20060301.144442.118975101.nemoto@toshiba-tops.co.jp>
Sender: linux-mips-bounce@linux-mips.org
Atsushi Nemoto writes:

> Hi.  I noticed that the 'jiffies' variable has 'wall_jiffies + 1'
> value in most of time.  I'm using MIPS platform but I think this is
> same for other platforms.
> 
> I suppose this is due to gcc does not know that jiffies_64 and jiffies
> share same place.

I can confirm that the same thing happens on powerpc, both 32-bit and
64-bit.  The compiler loads up jiffies, jiffies_64 and wall_jiffies
into registers before storing back the incremented value into
jiffies_64 and then updating wall_jiffies.

Thanks for finding that, it explains some other strange things that I
have seen happen.

Paul.

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