Date: Tue, 22 May 2007 15:51:35 -0700
From: Stephane Eranian <eranian@hpl.hp.com>
To: Andrew Morton <akpm@linux-foundation.org>
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: <20070522225135.GF28287@frankl.hpl.hp.com>
Reply-To: eranian@hpl.hp.com
References: <20070522124713.GB27428@frankl.hpl.hp.com> <20070522090210.1388ff3e.akpm@linux-foundation.org> <20070522160737.GI27631@frankl.hpl.hp.com> <20070522091517.251cc2d0.akpm@linux-foundation.org>
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Andrew,

On Tue, May 22, 2007 at 09:15:17AM -0700, Andrew Morton wrote:
> On Tue, 22 May 2007 09:07:37 -0700
> Stephane Eranian <eranian@hpl.hp.com> wrote:
> 
> > Andrew,
> > 
> > On Tue, May 22, 2007 at 09:02:10AM -0700, Andrew Morton wrote:
> > > 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.
> > 
> > Yes, and that is with the old IA-64 code. In the new one I used a dedicated
> > TIF flag.
> > 
> > Shall we just get rid of the flag, then?
> > 
> 
> I'd say so, yes.

Do you want a single patch or small patches broken-down by arch (and there are many...)?

-- 
-Stephane
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