Unverified Commit 7845f522 authored Apr 24, 2024 by Palmer Dabbelt

Merge patch series "riscv: enable lockless lockref implementation"

Jisheng Zhang <jszhang@kernel.org> says:

This series selects ARCH_USE_CMPXCHG_LOCKREF to enable the
cmpxchg-based lockless lockref implementation for riscv. Then,
implement arch_cmpxchg64_{relaxed|acquire|release}.

After patch1:
Using Linus' test case[1] on TH1520 platform, I see a 11.2% improvement.
On JH7110 platform, I see 12.0% improvement.

After patch2:
on both TH1520 and JH7110 platforms, I didn't see obvious
performance improvement with Linus' test case [1]. IMHO, this may
be related with the fence and lr.d/sc.d hw implementations. In theory,
lr/sc without fence could give performance improvement over lr/sc plus
fence, so add the code here to leave performance improvement room on
newer HW platforms.

* b4-shazam-merge:
  riscv: cmpxchg: implement arch_cmpxchg64_{relaxed|acquire|release}
  riscv: select ARCH_USE_CMPXCHG_LOCKREF

Link: http://marc.info/?l=linux-fsdevel&m=137782380714721&w=4 [1]
Link: https://lore.kernel.org/r/20240325111038.1700-1-jszhang@kernel.org


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

parents dcb2743d 79d6e4ea

arch/riscv/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -57,6 +57,7 @@ config RISCV
		select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU
		select ARCH_SUPPORTS_PER_VMA_LOCK if MMU
		select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK
		select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
		select ARCH_USE_MEMTEST
		select ARCH_USE_QUEUED_RWLOCKS
		select ARCH_USES_CFI_TRAPS if CFI_CLANG

arch/riscv/include/asm/cmpxchg.h

+18 −0

Original line number	Diff line number	Diff line
		@@ -203,4 +203,22 @@
		arch_cmpxchg_relaxed((ptr), (o), (n)); \
		})

		#define arch_cmpxchg64_relaxed(ptr, o, n) \
		({ \
		BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
		arch_cmpxchg_relaxed((ptr), (o), (n)); \
		})

		#define arch_cmpxchg64_acquire(ptr, o, n) \
		({ \
		BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
		arch_cmpxchg_acquire((ptr), (o), (n)); \
		})

		#define arch_cmpxchg64_release(ptr, o, n) \
		({ \
		BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
		arch_cmpxchg_release((ptr), (o), (n)); \
		})

		#endif /* _ASM_RISCV_CMPXCHG_H */