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Message-ID: <3113192.5fSG56mABF@diego>
Date: Tue, 14 Jun 2022 18:26:51 +0200
From: Heiko Stübner <heiko@...ech.de>
To: linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Cc: Dao Lu <daolu@...osinc.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Atish Patra <atishp@...shpatra.org>,
Anup Patel <anup@...infault.org>,
Randy Dunlap <rdunlap@...radead.org>,
Rob Herring <robh@...nel.org>,
Alexandre Ghiti <alexandre.ghiti@...onical.com>,
Qinglin Pan <panqinglin2020@...as.ac.cn>,
Tsukasa OI <research_trasio@....a4lg.com>,
Jisheng Zhang <jszhang@...nel.org>,
"open list:RISC-V ARCHITECTURE" <linux-riscv@...ts.infradead.org>,
Dao Lu <daolu@...osinc.com>
Subject: Re: [PATCH v2] arch/riscv: add Zihintpause support
Am Dienstag, 24. Mai 2022, 23:19:50 CEST schrieb Dao Lu:
> Implement support for the ZiHintPause extension.
>
> The PAUSE instruction is a HINT that indicates the current hart’s rate of
> instruction retirement should be temporarily reduced or paused.
>
> Reviewed-by: Heiko Stuebner <heiko@...ech.de>
> Tested-by: Heiko Stuebner <heiko@...ech.de>
> Signed-off-by: Dao Lu <daolu@...osinc.com>
> ---
>
> v1 -> v2:
> Remove the usage of static branch, use PAUSE if toolchain supports it
>
> arch/riscv/Makefile | 4 ++++
> arch/riscv/include/asm/hwcap.h | 1 +
> arch/riscv/include/asm/vdso/processor.h | 8 +++++++-
> arch/riscv/kernel/cpu.c | 1 +
> arch/riscv/kernel/cpufeature.c | 2 ++
> 5 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 7d81102cffd4..900a8fda1a2d 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -56,6 +56,10 @@ riscv-march-$(CONFIG_RISCV_ISA_C) := $(riscv-march-y)c
> toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
> riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
>
> +# Check if the toolchain supports Zihintpause extension
> +toolchain-supports-zihintpause := $(call cc-option-yn, -march=$(riscv-march-y)_zihintpause)
> +riscv-march-$(toolchain-supports-zihintpause) := $(riscv-march-y)_zihintpause
> +
> KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
> KBUILD_AFLAGS += -march=$(riscv-march-y)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 0734e42f74f2..caa9ee5459b4 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -52,6 +52,7 @@ extern unsigned long elf_hwcap;
> */
> enum riscv_isa_ext_id {
> RISCV_ISA_EXT_SSCOFPMF = RISCV_ISA_EXT_BASE,
svpbmt got merged meanwhile, so this patch needs a rebase
onto 5.19-rc.
One more nit below
> + RISCV_ISA_EXT_ZIHINTPAUSE,
> RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
> };
>
> diff --git a/arch/riscv/include/asm/vdso/processor.h b/arch/riscv/include/asm/vdso/processor.h
> index 134388cbaaa1..4de911a25051 100644
> --- a/arch/riscv/include/asm/vdso/processor.h
> +++ b/arch/riscv/include/asm/vdso/processor.h
> @@ -8,7 +8,13 @@
>
> static inline void cpu_relax(void)
> {
> -#ifdef __riscv_muldiv
> +#ifdef __riscv_zihintpause
> + /*
> + * Reduce instruction retirement.
> + * This assumes the PC changes.
> + */
> + __asm__ __volatile__ ("pause");
> +#elif __riscv_muldiv
> int dummy;
> /* In lieu of a halt instruction, induce a long-latency stall. */
> __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index ccb617791e56..89e563e9c4cc 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -88,6 +88,7 @@ int riscv_of_parent_hartid(struct device_node *node)
> */
> static struct riscv_isa_ext_data isa_ext_arr[] = {
> __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
> + __RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
> __RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
> };
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 1b2d42d7f589..37ff06682ae6 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -25,6 +25,7 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
> __ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
> #endif
>
> +
this is an unrelated change and also is adding an unneeded extra empty line.
Heiko
> /**
> * riscv_isa_extension_base() - Get base extension word
> *
> @@ -192,6 +193,7 @@ void __init riscv_fill_hwcap(void)
> set_bit(*ext - 'a', this_isa);
> } else {
> SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
> + SET_ISA_EXT_MAP("zihintpause", RISCV_ISA_EXT_ZIHINTPAUSE);
> }
> #undef SET_ISA_EXT_MAP
> }
>
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