Hi,
This started off as an effort to convert a cmpxchg based loop in arc/kernel/smp.c
to an API which is more LLOCK/SCOND friendly.
e.g.
do {
new = old = ACCESS_ONCE(*ipi_data_ptr);
new |= 1U << msg;
} while (cmpxchg(ipi_data_ptr, old, new) != old);
The generated code is horrible. There are 2 useless branches here and a
LD/LLOCK to same address all inside a loop.
8015cefc: ld_s r2,[r3,0]
8015cefe: or r5,r2,r1
8015cf02: llock r4,[r3]
8015cf06: brne r4,r2,8015cf12
8015cf0a: scond r5,[r3]
8015cf0e: bnz 8015cf02
8015cf12: brne r2,r4,8015cefc
An atomic_or() kind of API is better suited to generate something like below
8015cf02: llock r4,[r3]
8015cf06: or r5,r2,r1
8015cf0a: scond r5,[r3]
8015cf0e: bnz 8015cf02
Although this doesn't work for the specific instance I wanted to fix as
ipi_data_ptr is not atomic_t, I did run into a few things which could be
improved, hence this series.
Compile tested on ARC, ARM, x86.
I do have some concern about mixing long and int on 64 bit arch, which I've
captured inline in patch 2/3. It is most likely a lack of understand on my
part, but worth asking..
Thx,
-Vineet
Vineet Gupta (3):
asm-generic/atomic.h: ARCH_HAS_ATOMIC_OR -> CONFIG_ARCH_HAS_ATOMIC_OR
brcmfmac: dhd_sdio.c: use existing atomic_or primitive
ARC: provide atomic_or() and define ARCH_HAS_ATOMIC_OR
arch/arc/include/asm/atomic.h | 9 +++++++++
drivers/net/wireless/brcm80211/brcmfmac/sdio.c | 13 ++-----------
include/asm-generic/atomic.h | 2 +-
include/linux/atomic.h | 4 ++--
4 files changed, 14 insertions(+), 14 deletions(-)
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
