@@ -115,6 +115,26 @@ config UPROBES
managed by the kernel and kept transparent to the probed
application. )
+config 64BIT_ATOMIC_ACCESS
+ def_bool 64BIT
+ help
+ On some 32bit architectures as well as 64bit architectures,
+ 64bit accesses are atomic when certain conditions are satisfied.
+
+ This symbol should be selected by an architecture if 64 bit
+ accesses can be atomic.
+
+config 64BIT_ATOMIC_ALIGNED_ACCESS
+ def_bool n
+ depends on 64BIT_ATOMIC_ACCESS
+ help
+ On 64BIT_ATOMIC_ACCESS enabled system, the address should be
+ aligned by 8 to guarantee the accesses are atomic.
+
+ This symbol should be selected by an architecture if 64 bit
+ accesses are required to be 64 bit aligned to guarantee that
+ the 64bit accesses are atomic.
+
config HAVE_64BIT_ALIGNED_ACCESS
def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
help
On some 32-bit architectures, 64bit accesses are atomic when certain conditions are satisfied. For example, on LPAE (Large Physical Address Extension) enabled ARM architecture, 'ldrd/strd' (load/store doublewords) instructions are 64bit atomic as long as the address is 64-bit aligned. This feature is to guarantee atomic accesses on newly introduced 64bit wide descriptors in the translation tables, and 's/u64' variables can be accessed atomically when they are aligned(8) on LPAE enabled ARM architecture machines. Introducing 64BIT_ATOMIC_ACCESS and 64BIT_ATOMIC_ALIGNED_ACCESS, which can be true for the 32bit architectures as well as 64bit architectures, we can optimize some kernel codes using seqlock (timekeeping) or mimics of it (like in sched/cfq) simply to read or write 64bit variables. The existing codes depend on CONFIG_64BIT to determine whether the 64bit variables can be directly accessed or need additional synchronization primitives like seqlock. CONFIG_64BIT_ATOMIC_ACCESS can be used instead of CONFIG_64BIT in the cases. 64BIT_ATOMIC_ALIGNED_ACCESS can be used in the variable declaration to indicate the alignment requirement to the compiler (__attribute__((aligned(8)))) in the way of #ifdef. Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com> --- arch/Kconfig | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)