From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Date: Tue, 22 May 2007 16:02:10 +0000 Subject: Re: is TIF_NOTIFY_RESUME used? Message-Id: <20070522090210.1388ff3e.akpm@linux-foundation.org> List-Id: References: <20070522124713.GB27428@frankl.hpl.hp.com> In-Reply-To: <20070522124713.GB27428@frankl.hpl.hp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: eranian@hpl.hp.com Cc: linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, ak@suse.de, tony.luck@intel.com On Tue, 22 May 2007 05:47:13 -0700 Stephane Eranian 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.