From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C049241E3; Thu, 14 Sep 2023 14:04:08 +0000 (UTC) Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4735D1A2; Thu, 14 Sep 2023 07:04:07 -0700 (PDT) Received: from kwepemi500020.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Rmf8y1GDlzGppB; Thu, 14 Sep 2023 22:00:18 +0800 (CST) Received: from [10.67.109.184] (10.67.109.184) by kwepemi500020.china.huawei.com (7.221.188.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Thu, 14 Sep 2023 22:04:01 +0800 Message-ID: Date: Thu, 14 Sep 2023 22:04:00 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: [PATCH bpf-next 4/6] riscv, bpf: Add necessary Zbb instructions Content-Language: en-US To: Conor Dooley , Conor Dooley CC: Pu Lehui , , , , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Palmer Dabbelt , Luke Nelson References: <20230913153413.1446068-1-pulehui@huaweicloud.com> <20230913153413.1446068-5-pulehui@huaweicloud.com> <20230913-granny-heat-35d70b49ac85@spud> <20230914-ought-hypnotize-64cee0e27ed2@wendy> From: Pu Lehui In-Reply-To: <20230914-ought-hypnotize-64cee0e27ed2@wendy> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.109.184] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemi500020.china.huawei.com (7.221.188.8) X-CFilter-Loop: Reflected On 2023/9/14 21:02, Conor Dooley wrote: > On Wed, Sep 13, 2023 at 05:23:48PM +0100, Conor Dooley wrote: >> On Wed, Sep 13, 2023 at 11:34:11PM +0800, Pu Lehui wrote: >>> From: Pu Lehui >>> >>> Add necessary Zbb instructions introduced by [0] to reduce code size and >>> improve performance of RV64 JIT. At the same time, a helper is added to >>> check whether the CPU supports Zbb instructions. >>> >>> [0] https://github.com/riscv/riscv-bitmanip/releases/download/1.0.0/bitmanip-1.0.0-38-g865e7a7.pdf >>> >>> Signed-off-by: Pu Lehui >>> --- >>> arch/riscv/net/bpf_jit.h | 26 ++++++++++++++++++++++++++ >>> 1 file changed, 26 insertions(+) >>> >>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h >>> index 8e0ef4d08..7ee59d1f6 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 rvzbb_enabled(void) >>> +{ >>> + return IS_ENABLED(CONFIG_RISCV_ISA_ZBB); >>> +} >> >> I dunno much about bpf, so passing question that may be a bit obvious: >> Is this meant to be a test as to whether the kernel binary is built with >> support for the extension, or whether the underlying platform is capable >> of executing zbb instructions. >> >> Sorry if that would be obvious to a bpf aficionado, context I have here >> is the later user and the above rvc_enabled() test, which functions >> differently to Zbb and so doesn't really help me. > > FTR, I got an off-list reply about this & it is meant to be a check as > to whether the underlying platform supports the extension. The current > test here is insufficient for that. > Thanks Conor for explain me lot about the difference between Compressed instructions and Zbb instructions. As the compressed instructions are a build-time option, while the Zbb is runtime detected. We need to add additional runtime detection as show bellow: riscv_has_extension_likely(RISCV_ISA_EXT_ZBB) will patch this suggestion to the next version. Thanks, Lehui. > Thanks, > Conor.