From: "Christoph Müllner" <christoph.muellner@vrull.eu>
To: libc-alpha@sourceware.org,
Adhemerval Zanella <adhemerval.zanella@linaro.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Darius Rad <darius@bluespec.com>,
Andrew Waterman <andrew@sifive.com>,
Philipp Tomsich <philipp.tomsich@vrull.eu>,
Evan Green <evan@rivosinc.com>,
Kito Cheng <kito.cheng@sifive.com>,
Jeff Law <jeffreyalaw@gmail.com>,
Vineet Gupta <vineetg@rivosinc.com>
Cc: "Christoph Müllner" <christoph.muellner@vrull.eu>
Subject: [PATCH] RISC-V: Execute a PAUSE hint in spin loops
Date: Thu, 18 Apr 2024 23:58:58 +0200 [thread overview]
Message-ID: <20240418215858.4151969-1-christoph.muellner@vrull.eu> (raw)
The atomic_spin_nop() macro can be used to run arch-specific
code in the body of a spin loop to potentially improve efficiency.
RISC-V's Zihintpause extension includes a PAUSE instruction for
this use-case, which is encoded as a HINT, which means that it
behaves like a NOP on systems that don't implement Zihintpause.
Binutils supports Zihintpause since 2.36, so this patch uses
the ".insn" directive to keep the code compatible with older
toolchains.
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
---
sysdeps/unix/sysv/linux/riscv/atomic-machine.h | 3 +++
1 file changed, 3 insertions(+)
diff --git a/sysdeps/unix/sysv/linux/riscv/atomic-machine.h b/sysdeps/unix/sysv/linux/riscv/atomic-machine.h
index c1c9d949a0..90283d9746 100644
--- a/sysdeps/unix/sysv/linux/riscv/atomic-machine.h
+++ b/sysdeps/unix/sysv/linux/riscv/atomic-machine.h
@@ -178,4 +178,7 @@
# error "ISAs that do not subsume the A extension are not supported"
#endif /* !__riscv_atomic */
+/* Execute a PAUSE hint when spinning. */
+#define atomic_spin_nop() __asm(".insn i 0x0f, 0, x0, x0, 0x010")
+
#endif /* bits/atomic.h */
--
2.44.0
next reply other threads:[~2024-04-18 21:59 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-18 21:58 Christoph Müllner [this message]
2024-04-19 1:03 ` Palmer Dabbelt
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