linux-kernel - Re: [PATCH v3] riscv, bpf: Optimize zextw insn with Zba extension

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Message-ID: <3d7bca4f-492a-46cb-b65f-0bf14da97bb2@huawei.com>
Date: Fri, 17 May 2024 15:24:03 +0800
From: Pu Lehui <pulehui@...wei.com>
To: Xiao Wang <xiao.w.wang@...el.com>
CC: <paul.walmsley@...ive.com>, <palmer@...belt.com>, <aou@...s.berkeley.edu>,
	<luke.r.nels@...il.com>, <xi.wang@...il.com>, <bjorn@...nel.org>,
	<ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
	<martin.lau@...ux.dev>, <eddyz87@...il.com>, <song@...nel.org>,
	<yonghong.song@...ux.dev>, <john.fastabend@...il.com>, <kpsingh@...nel.org>,
	<sdf@...gle.com>, <haoluo@...gle.com>, <jolsa@...nel.org>,
	<linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<bpf@...r.kernel.org>, <haicheng.li@...el.com>, <conor@...nel.org>,
	<ben.dooks@...ethink.co.uk>, <ajones@...tanamicro.com>
Subject: Re: [PATCH v3] riscv, bpf: Optimize zextw insn with Zba extension



On 2024/5/16 17:04, Xiao Wang wrote:
> The Zba extension provides add.uw insn which can be used to implement
> zext.w with rs2 set as ZERO.
> 
> Signed-off-by: Xiao Wang <xiao.w.wang@...el.com>
> ---
> v3:
> * Remove the Kconfig dependencies on TOOLCHAIN_HAS_ZBA and
>    RISCV_ALTERNATIVE. (Andrew)
> v2:
> * Add Zba description in the Kconfig. (Lehui)
> * Reword the Kconfig help message to make it clearer. (Conor)
> ---
>   arch/riscv/Kconfig       | 12 ++++++++++++
>   arch/riscv/net/bpf_jit.h | 18 ++++++++++++++++++
>   2 files changed, 30 insertions(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 6bec1bce6586..b64d55dc929f 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -601,6 +601,18 @@ config TOOLCHAIN_HAS_VECTOR_CRYPTO
>   	def_bool $(as-instr, .option arch$(comma) +v$(comma) +zvkb)
>   	depends on AS_HAS_OPTION_ARCH
>   
> +config RISCV_ISA_ZBA
> +	bool "Zba extension support for bit manipulation instructions"
> +	default y
> +	help
> +	   Add support for enabling optimisations in the kernel when the Zba
> +	   extension is detected at boot.
> +
> +	   The Zba extension provides instructions to accelerate the generation
> +	   of addresses that index into arrays of basic data types.
> +
> +	   If you don't know what to do here, say Y.
> +
>   config RISCV_ISA_ZBB
>   	bool "Zbb extension support for bit manipulation instructions"
>   	depends on TOOLCHAIN_HAS_ZBB
> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
> index f4b6b3b9edda..18a7885ba95e 100644
> --- a/arch/riscv/net/bpf_jit.h
> +++ b/arch/riscv/net/bpf_jit.h
> @@ -18,6 +18,11 @@ static inline bool rvc_enabled(void)
>   	return IS_ENABLED(CONFIG_RISCV_ISA_C);
>   }
>   
> +static inline bool rvzba_enabled(void)
> +{
> +	return IS_ENABLED(CONFIG_RISCV_ISA_ZBA) && riscv_has_extension_likely(RISCV_ISA_EXT_ZBA);
> +}
> +
>   static inline bool rvzbb_enabled(void)
>   {
>   	return IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && riscv_has_extension_likely(RISCV_ISA_EXT_ZBB);
> @@ -937,6 +942,14 @@ static inline u16 rvc_sdsp(u32 imm9, u8 rs2)
>   	return rv_css_insn(0x7, imm, rs2, 0x2);
>   }
>   
> +/* RV64-only ZBA instructions. */
> +
> +static inline u32 rvzba_zextw(u8 rd, u8 rs1)
> +{
> +	/* add.uw rd, rs1, ZERO */
> +	return rv_r_insn(0x04, RV_REG_ZERO, rs1, 0, rd, 0x3b);
> +}
> +
>   #endif /* __riscv_xlen == 64 */
>   
>   /* Helper functions that emit RVC instructions when possible. */
> @@ -1159,6 +1172,11 @@ static inline void emit_zexth(u8 rd, u8 rs, struct rv_jit_context *ctx)
>   
>   static inline void emit_zextw(u8 rd, u8 rs, struct rv_jit_context *ctx)
>   {
> +	if (rvzba_enabled()) {
> +		emit(rvzba_zextw(rd, rs), ctx);
> +		return;
> +	}
> +
>   	emit_slli(rd, rs, 32, ctx);
>   	emit_srli(rd, rd, 32, ctx);
>   }
Reviewed-by: Pu Lehui <pulehui@...wei.com>
Tested-by: Pu Lehui <pulehui@...wei.com>