@@ -654,6 +654,18 @@ config RISCV_MISALIGNED
load/store for both kernel and userspace. When disable, misaligned
accesses will generate SIGBUS in userspace and panic in kernel.
+config RISCV_EFFICIENT_UNALIGNED_ACCESS
+ bool "Use unaligned access for some functions"
+ depends on NONPORTABLE
+ select HAVE_EFFICIENT_UNALIGNED_ACCESS
+ default n
+ help
+ Say Y here if you want the kernel only run on hardware platforms which
+ support efficient unaligned access, then unaligned access will be used
+ in some functions for optimized performance.
+
+ If unsure what to do here, say N.
+
endmenu # "Platform type"
menu "Kernel features"
Some riscv implementations such as T-HEAD's C906, C908, C910 and C920 supports efficient unaligned access, for performance reason we want to enable HAVE_EFFICIENT_UNALIGNED_ACCESS on these platforms. To avoid performance regressions on other non efficient unaligned access platforms, HAVE_EFFICIENT_UNALIGNED_ACCESS can't be globaly selected. To solve this problem, runtime code patching based on the detected speed is a good solution. But that's not easy, it involves lots of work to modify vairous subsystems such as net, mm, lib and so on. This can be done step by step. Now let's introduce RISCV_EFFICIENT_UNALIGNED_ACCESS which depends on NONPORTABLE, if users know during config time that the kernel will be only run on those efficient unaligned access hw platforms, they can enable it. Obviously, generic unified kernel Image should enable it. Signed-off-by: Jisheng Zhang <jszhang@kernel.org> --- arch/riscv/Kconfig | 12 ++++++++++++ 1 file changed, 12 insertions(+)