Date: Tue, 22 May 2007 09:02:10 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: eranian@hpl.hp.com
Cc: linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, ak@suse.de,
       tony.luck@intel.com
Subject: Re: is TIF_NOTIFY_RESUME used?
Message-Id: <20070522090210.1388ff3e.akpm@linux-foundation.org>
In-Reply-To: <20070522124713.GB27428@frankl.hpl.hp.com>
References: <20070522124713.GB27428@frankl.hpl.hp.com>
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On Tue, 22 May 2007 05:47:13 -0700
Stephane Eranian <eranian@hpl.hp.com> wrote:

> Hello,
> 
> For perfmon, we need a couple of TIF bits. It seems that with 2.6.22-rc2
> there is now a TIF_RESTORE_SIGMASK which uses the last remaining bit in the
> first 7 bits of the thread flag. Many architectures, including IA-64, rely
> on the fact that some of the TIF flags (TIF_ALL_WORKMASK or TIF_ALL_WORK)
> tested on kernel exit reside in the low 8-bit or 7-bit because they use
> instructions (such as add r1=imm8,r2 on IA-64) which operate on 8 or 7 bit
> immediate.
> 
> On IA-64, adding that one perfmon flag (as bit 7) would cause some
> restructuring in the kernel exit path but also in all the lightweight syscall
> handlers.
> 
> I looked at all the low order TIF flags and found that TIF_NOTIFY_RESUME 
> was never set nor used anywhere in any architecture. Is that really the case?
> 
> If so, we could get rid of it and free up one low-order TIF bit.
> 

My grepping argees with yours.  The only place where TIF_NOTIFY_RESUME gets
altered is in ./arch/ia64/kernel/perfmon.c.
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