linux-kernel - [PATCH 0/2] riscv: introduce percpu.h

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Message-Id: <20250819135007.85646-1-cuiyunhui@bytedance.com>
Date: Tue, 19 Aug 2025 21:50:05 +0800
From: Yunhui Cui <cuiyunhui@...edance.com>
To: yury.norov@...il.com,
	linux@...musvillemoes.dk,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	dennis@...nel.org,
	tj@...nel.org,
	cl@...two.org,
	linux-mm@...ck.org
Cc: Yunhui Cui <cuiyunhui@...edance.com>
Subject: [PATCH 0/2] riscv: introduce percpu.h

Current per-CPU operations rely on generic code using raw_local_irq_save(),
which incurs significant overhead. This patch optimizes 32/64-bit paths with
RISC-V atomic instructions, reducing overhead.

RISC-V lacks lr/sc.b/h support; without ZABHA, emulating 8/16-bit operations
via lr/sc.w would require complex mask logic. However, data shows 8/16-bit
per-CPU operations are extremely rare (single-digit counts in boot and
hackbench tests). Thus, we let 8/16-bit ops fall back to the generic
implementation, avoiding unnecessary complexity. 32/64-bit ops use direct
atomic instructions for performance.

Yunhui Cui (2):
  riscv: remove irqflags.h inclusion in asm/bitops.h
  riscv: introduce percpu.h into include/asm

 arch/riscv/include/asm/bitops.h |   1 -
 arch/riscv/include/asm/percpu.h | 138 ++++++++++++++++++++++++++++++++
 2 files changed, 138 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/percpu.h

-- 
2.39.5