linux-kernel - Re: is TIF_NOTIFY

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Message-Id: <20070522160207.e147a8a6.akpm@linux-foundation.org>
Date:	Tue, 22 May 2007 16:02:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	eranian@....hp.com
Cc:	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	ak@...e.de, tony.luck@...el.com
Subject: Re: is TIF_NOTIFY_RESUME used?

On Tue, 22 May 2007 15:51:35 -0700
Stephane Eranian <eranian@....hp.com> wrote:

> 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@....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@....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...)?

One patch is OK for this, thanks.
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