From 48b4fc66939d5ed49da305cad9788dcd953b5cd2 Mon Sep 17 00:00:00 2001 From: Jisheng Zhang Date: Mon, 25 Mar 2024 18:58:23 +0800 Subject: riscv: select ARCH_HAS_FAST_MULTIPLIER Currently, riscv linux requires at least IMA, so all platforms have a multiplier. And I assume the 'mul' efficiency is comparable or better than a sequence of five or so register-dependent arithmetic instructions. Select ARCH_HAS_FAST_MULTIPLIER to get slightly nicer codegen. Refer to commit f9b4192923fa ("[PATCH] bitops: hweight() speedup") for more details. In a simple benchmark test calling hweight64() in a loop, it got: about 14% performance improvement on JH7110, tested on Milkv Mars. about 23% performance improvement on TH1520 and SG2042, tested on Sipeed LPI4A and SG2042 platform. a slight performance drop on CV1800B, tested on milkv duo. Among all riscv platforms in my hands, this is the only one which sees a slight performance drop. It means the 'mul' isn't quick enough. However, the situation exists on x86 too, for example, P4 doesn't have fast integer multiplies as said in the above commit, x86 also selects ARCH_HAS_FAST_MULTIPLIER. So let's select ARCH_HAS_FAST_MULTIPLIER which can benefit almost riscv platforms. Samuel also provided some performance numbers: On Unmatched: 20% speedup for __sw_hweight32 and 30% speedup for __sw_hweight64. On D1: 8% speedup for __sw_hweight32 and 8% slowdown for __sw_hweight64. Signed-off-by: Jisheng Zhang Reviewed-by: Samuel Holland Tested-by: Samuel Holland Reviewed-by: Alexandre Ghiti Link: https://lore.kernel.org/r/20240325105823.1483-1-jszhang@kernel.org Signed-off-by: Palmer Dabbelt --- arch/riscv/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/riscv') diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 2dac484ea645..6bec1bce6586 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -23,6 +23,7 @@ config RISCV select ARCH_HAS_DEBUG_VIRTUAL if MMU select ARCH_HAS_DEBUG_VM_PGTABLE select ARCH_HAS_DEBUG_WX + select ARCH_HAS_FAST_MULTIPLIER select ARCH_HAS_FORTIFY_SOURCE select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_GIGANTIC_PAGE -- cgit v1.2.3