netdev - Re: [PATCH bpf-next v2 6/6] riscv, bpf: Optimize bswap insns with Zbb support

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Message-ID: <c33984f0-57dc-4833-a96d-164425fc7578@huaweicloud.com>
Date: Mon, 15 Jan 2024 20:26:43 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: Björn Töpel <bjorn@...nel.org>, bpf@...r.kernel.org,
 linux-riscv@...ts.infradead.org, netdev@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>,
 KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
 Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, Conor Dooley <conor@...nel.org>,
 Luke Nelson <luke.r.nels@...il.com>, Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next v2 6/6] riscv, bpf: Optimize bswap insns with Zbb
 support



On 2023/9/28 19:08, Björn Töpel wrote:
> Pu Lehui <pulehui@...weicloud.com> writes:
> 
>> From: Pu Lehui <pulehui@...wei.com>
>>
>> Optimize bswap instructions by rev8 Zbb instruction conbined with srli
>> instruction. And Optimize 16-bit zero-extension with Zbb support.
>>
>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>> ---
>>   arch/riscv/net/bpf_jit.h        | 67 +++++++++++++++++++++++++++++++++
>>   arch/riscv/net/bpf_jit_comp64.c | 50 +-----------------------
>>   2 files changed, 69 insertions(+), 48 deletions(-)
>>
>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
>> index 944bdd6e4..a04eed672 100644
>> --- a/arch/riscv/net/bpf_jit.h
>> +++ b/arch/riscv/net/bpf_jit.h
>> @@ -1135,12 +1135,79 @@ static inline void emit_sextw(u8 rd, u8 rs, struct rv_jit_context *ctx)
>>   	emit_addiw(rd, rs, 0, ctx);
>>   }
>>   
>> +static inline void emit_zexth(u8 rd, u8 rs, struct rv_jit_context *ctx)
>> +{
>> +	if (rvzbb_enabled()) {
>> +		emit(rvzbb_zexth(rd, rs), ctx);
>> +	} else {
>> +		emit_slli(rd, rs, 48, ctx);
>> +		emit_srli(rd, rd, 48, ctx);
>> +	}
>> +}
>> +
> 
> Prefer early-exit.
> 
>>   static inline void emit_zextw(u8 rd, u8 rs, struct rv_jit_context *ctx)
>>   {
>>   	emit_slli(rd, rs, 32, ctx);
>>   	emit_srli(rd, rd, 32, ctx);
>>   }
>>   
>> +static inline void emit_bswap(u8 rd, s32 imm, struct rv_jit_context *ctx)
>> +{
>> +	if (rvzbb_enabled()) {
>> +		int bits = 64 - imm;
>> +
>> +		emit(rvzbb_rev8(rd, rd), ctx);
>> +		if (bits)
>> +			emit_srli(rd, rd, bits, ctx);
>> +	} else {
>> +		emit_li(RV_REG_T2, 0, ctx);
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +		if (imm == 16)
>> +			goto out_be;
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +		if (imm == 32)
>> +			goto out_be;
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +		emit_slli(RV_REG_T2, RV_REG_T2, 8, ctx);
>> +		emit_srli(rd, rd, 8, ctx);
>> +out_be:
>> +		emit_andi(RV_REG_T1, rd, 0xff, ctx);
>> +		emit_add(RV_REG_T2, RV_REG_T2, RV_REG_T1, ctx);
>> +
>> +		emit_mv(rd, RV_REG_T2, ctx);
>> +	}
>> +}
> 
> Definitely early-exit for this one!
> 
> This function really show-cases why ZBB is nice! ;-)
> 
> I'll take the next rev of series for a test!
> 

Okay, the relevant modifications will be presented in v3 and will be 
sent soon.

> 
> Björn