This change is similar to e001bbae71
ARM: cmpxchg: avoid warnings from macro-ized cmpxchg() implementations
A recent change in kernel/acct.c added a new warning for many
configurations using generic __xchg() implementation:
In file included from ./arch/nios2/include/asm/cmpxchg.h:12:0,
from include/asm-generic/atomic.h:18,
from arch/nios2/include/generated/asm/atomic.h:1,
from include/linux/atomic.h:4,
from include/linux/spinlock.h:406,
from include/linux/mmzone.h:7,
from include/linux/gfp.h:5,
from include/linux/mm.h:9,
from kernel/acct.c:46:
kernel/acct.c: In function 'acct_pin_kill':
include/asm-generic/cmpxchg.h:94:3: warning: value computed is not used [-Wunused-value]
((__typeof__(*(ptr)))__cmpxchg_local_generic((ptr), (unsigned long)(o),\
^
include/asm-generic/cmpxchg.h:102:28: note: in expansion of macro 'cmpxchg_local'
#define cmpxchg(ptr, o, n) cmpxchg_local((ptr), (o), (n))
^
kernel/acct.c:177:2: note: in expansion of macro 'cmpxchg'
cmpxchg(&acct->ns->bacct, pin, NULL);
^
The code is in fact correct, it's just a cmpxchg() call that
intentionally ignores the result, and no other code does that. The
warning does not show up on x86 because of the way that its cmpxchg()
macro is written. This changes the asm-ggeneric implementation to use
a similar construct with a compound expression instead of a typecast,
which causes the compiler to not complain about an unused result.
Fix the other macros in this file in a similar way, and place them
just below their function implementations.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
The rtmutex code is the only user of __HAVE_ARCH_CMPXCHG and we have a few
other user of cmpxchg() which do not care about __HAVE_ARCH_CMPXCHG. This
define was first introduced in 23f78d4a0 ("[PATCH] pi-futex: rt mutex core")
which is v2.6.18. The generic cmpxchg was introduced later in 068fbad288
("Add cmpxchg_local to asm-generic for per cpu atomic operations") which is
v2.6.25.
Back then something was required to get rtmutex working with the fast
path on architectures without cmpxchg and this seems to be the result.
It popped up recently on rt-users because ARM (v6+) does not define
__HAVE_ARCH_CMPXCHG (even that it implements it) which results in slower
locking performance in the fast path.
To put some numbers on it: preempt -RT, am335x, 10 loops of
100000 invocations of rt_spin_lock() + rt_spin_unlock() (time "total" is
the average of the 10 loops for the 100000 invocations, "loop" is
"total / 100000 * 1000"):
cmpxchg | slowpath used || cmpxchg used
| total | loop || total | loop
--------|-----------|-------||------------|-------
ARMv6 | 9129.4 us | 91 ns || 3311.9 us | 33 ns
generic | 9360.2 us | 94 ns || 10834.6 us | 108 ns
----------------------------||--------------------
Forcing it to generic cmpxchg() made things worse for the slowpath and
even worse in cmpxchg() path. It boils down to 14ns more per lock+unlock
in a cache hot loop so it might not be that much in real world.
The last test was a substitute for pre ARMv6 machine but then I was able
to perform the comparison on imx28 which is ARMv5 and therefore is
always is using the generic cmpxchg implementation. And the numbers:
| total | loop
-------- |----------- |--------
slowpath | 263937.2 us | 2639 ns
cmpxchg | 16934.2 us | 169 ns
--------------------------------
The numbers are larger since the machine is slower in general. However,
letting rtmutex use cmpxchg() instead the slowpath seem to improve things.
Since from the ARM (tested on am335x + imx28) point of view always
using cmpxchg() in rt_mutex_lock() + rt_mutex_unlock() makes sense I
would drop the define.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: will.deacon@arm.com
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20150225175613.GE6823@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
asm/cmpxchg.h can be included on its own and needs to be self-consistent.
The definitions for the cmpxchg*_local macros, as such, need to be part
of this file.
This fixes a build issue on OpenRISC since the system.h smashing patch
96f951edb1 that introdued the direct inclusion
asm/cmpxchg.h into linux/llist.h.
CC: David Howells <dhowells@redhat.com>
Signed-off-by: Jonas Bonn <jonas@southpole.se>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Builds of the openrisc or1ksim_defconfig show the following:
In file included from arch/openrisc/include/generated/asm/cmpxchg.h:1:0,
from include/asm-generic/atomic.h:18,
from arch/openrisc/include/generated/asm/atomic.h:1,
from include/linux/atomic.h:4,
from include/linux/dcache.h:4,
from fs/notify/fsnotify.c:19:
include/asm-generic/cmpxchg.h: In function '__xchg':
include/asm-generic/cmpxchg.h:34:20: error: expected ')' before 'u8'
include/asm-generic/cmpxchg.h:34:20: warning: type defaults to 'int' in type name
and many more lines of similar errors. It seems specific to the or32
because most other platforms have an arch specific component that would
have already included types.h ahead of time, but the o32 does not.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jonas Bonn <jonas@southpole.se>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: David Howells <dhowells@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Move the asm-generic/system.h xchg() implementation to asm-generic/cmpxchg.h
to simplify disintegration of asm/system.h.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Make asm-generic/cmpxchg.h #include asm-generic/cmpxchg-local.h as all arch
files that #include the former also #include the latter. See:
grep -rl asm-generic/cmpxchg-local[.]h arch/ | sort > b
grep -rl asm-generic/cmpxchg[.]h arch/ | sort > a
comm a b
This simplifies the disintegration of asm-generic/system.h for arches that
don't have their own.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Marek Vasut