Commit 3a6bfbc9 authored Jun 29, 2014 by Davidlohr Bueso Committed by Ingo Molnar Jul 17, 2014

arch, locking: Ciao arch_mutex_cpu_relax()



The arch_mutex_cpu_relax() function, introduced by 34b133f8, is
hacky and ugly. It was added a few years ago to address the fact
that common cpu_relax() calls include yielding on s390, and thus
impact the optimistic spinning functionality of mutexes. Nowadays
we use this function well beyond mutexes: rwsem, qrwlock, mcs and
lockref. Since the macro that defines the call is in the mutex header,
any users must include mutex.h and the naming is misleading as well.

This patch (i) renames the call to cpu_relax_lowlatency  ("relax, but
only if you can do it with very low latency") and (ii) defines it in
each arch's asm/processor.h local header, just like for regular cpu_relax
functions. On all archs, except s390, cpu_relax_lowlatency is simply cpu_relax,
and thus we can take it out of mutex.h. While this can seem redundant,
I believe it is a good choice as it allows us to move out arch specific
logic from generic locking primitives and enables future(?) archs to
transparently define it, similarly to System Z.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Anton Blanchard <anton@samba.org>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Bharat Bhushan <r65777@freescale.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Liqin <liqin.linux@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Howells <dhowells@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
Cc: Dominik Dingel <dingel@linux.vnet.ibm.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Joseph Myers <joseph@codesourcery.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Cc: Lennox Wu <lennox.wu@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Salter <msalter@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Qais Yousef <qais.yousef@imgtec.com>
Cc: Qiaowei Ren <qiaowei.ren@intel.com>
Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Steven Miao <realmz6@gmail.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Stratos Karafotis <stratosk@semaphore.gr>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vasily Kulikov <segoon@openwall.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: adi-buildroot-devel@lists.sourceforge.net
Cc: linux390@de.ibm.com
Cc: linux-alpha@vger.kernel.org
Cc: linux-am33-list@redhat.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-cris-kernel@axis.com
Cc: linux-hexagon@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux@lists.openrisc.net
Cc: linux-m32r-ja@ml.linux-m32r.org
Cc: linux-m32r@ml.linux-m32r.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-metag@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1404079773.2619.4.camel@buesod1.americas.hpqcorp.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent acf59377

arch/alpha/include/asm/processor.h

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -57,6 +57,7 @@ unsigned long get_wchan(struct task_struct *p);
	((tsk) == current ? rdusp() : task_thread_info(tsk)->pcb.usp)		((tsk) == current ? rdusp() : task_thread_info(tsk)->pcb.usp)

	#define cpu_relax() barrier()		#define cpu_relax() barrier()
			#define cpu_relax_lowlatency() cpu_relax()

	#define ARCH_HAS_PREFETCH		#define ARCH_HAS_PREFETCH
	#define ARCH_HAS_PREFETCHW		#define ARCH_HAS_PREFETCHW

arch/arc/include/asm/processor.h

+2 −0

Original line number	Original line	Diff line number	Diff line
	@@ -62,6 +62,8 @@ unsigned long thread_saved_pc(struct task_struct *t);
	#define cpu_relax() do { } while (0)		#define cpu_relax() do { } while (0)
	#endif		#endif

			#define cpu_relax_lowlatency() cpu_relax()

	#define copy_segments(tsk, mm) do { } while (0)		#define copy_segments(tsk, mm) do { } while (0)
	#define release_segments(mm) do { } while (0)		#define release_segments(mm) do { } while (0)

arch/arm/include/asm/processor.h

+2 −0

Original line number	Original line	Diff line number	Diff line
	@@ -82,6 +82,8 @@ unsigned long get_wchan(struct task_struct *p);
	#define cpu_relax() barrier()		#define cpu_relax() barrier()
	#endif		#endif

			#define cpu_relax_lowlatency() cpu_relax()

	#define task_pt_regs(p) \		#define task_pt_regs(p) \
	((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)		((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)

arch/arm64/include/asm/processor.h

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -129,6 +129,7 @@ extern void release_thread(struct task_struct *);
	unsigned long get_wchan(struct task_struct *p);		unsigned long get_wchan(struct task_struct *p);

	#define cpu_relax() barrier()		#define cpu_relax() barrier()
			#define cpu_relax_lowlatency() cpu_relax()

	/* Thread switching */		/* Thread switching */
	extern struct task_struct cpu_switch_to(struct task_struct prev,		extern struct task_struct cpu_switch_to(struct task_struct prev,

arch/avr32/include/asm/processor.h

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -92,6 +92,7 @@ extern struct avr32_cpuinfo boot_cpu_data;
	#define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))		#define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))

	#define cpu_relax() barrier()		#define cpu_relax() barrier()
			#define cpu_relax_lowlatency() cpu_relax()
	#define cpu_sync_pipeline() asm volatile("sub pc, -2" : : : "memory")		#define cpu_sync_pipeline() asm volatile("sub pc, -2" : : : "memory")

	struct cpu_context {		struct cpu_context {