netdev - Re: [PATCH bpf-next 2/5] riscv, bpf: Relax restrictions on Zbb instructions

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Message-ID: <bb6e839e-c840-4374-8014-5493cad45bdc@huaweicloud.com>
Date: Wed, 3 Apr 2024 18:19:05 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: Daniel Borkmann <daniel@...earbox.net>, Björn Töpel
 <bjorn@...nel.org>, bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
 netdev@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, 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>, Mykola Lysenko <mykolal@...com>,
 Manu Bretelle <chantr4@...il.com>, Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next 2/5] riscv, bpf: Relax restrictions on Zbb
 instructions



On 2024/4/3 0:03, Daniel Borkmann wrote:
> On 4/2/24 4:27 PM, Björn Töpel wrote:
>> Pu Lehui <pulehui@...weicloud.com> writes:
>>> From: Pu Lehui <pulehui@...wei.com>
>>>
>>> This patch relaxes the restrictions on the Zbb instructions. The 
>>> hardware
>>> is capable of recognizing the Zbb instructions independently, 
>>> eliminating
>>> the need for reliance on kernel compile configurations.
>>>
>>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>>
>> Should this patch really be part of this series?
> 
> No, that should be submitted independently.
> 

My initial thought was that I didn't enable CONFIG_RISCV_ISA_ZBB in 
config.riscv64, so I should loosen this restriction to enable zbb 
optimization. It could not be part of this series.

By the way, after reading what Conor and Björn said, I think we should 
align with kernel sematic, that is, emit zbb when CONFIG_RISCV_ISA_ZBB 
is enabled and so that if Zbb is detected they can be used.

> Also, given Eduard's comment, it would be great if you could add the
> instructions to tools/testing/selftests/bpf/README.rst even if not in
> a perfect shape, but it would give developers a chance to get started.
> 
> Thanks,
> Daniel