From: Conor Dooley <conor@kernel.org> To: Stefan O'Rear <sorear@fastmail.com> Cc: "Pu Lehui" <pulehui@huaweicloud.com>, bpf@vger.kernel.org, linux-riscv@lists.infradead.org, netdev@vger.kernel.org, "Björn Töpel" <bjorn@kernel.org>, "Alexei Starovoitov" <ast@kernel.org>, "Daniel Borkmann" <daniel@iogearbox.net>, "Andrii Nakryiko" <andrii@kernel.org>, "Martin KaFai Lau" <martin.lau@linux.dev>, "Eduard Zingerman" <eddyz87@gmail.com>, "Song Liu" <song@kernel.org>, "Yonghong Song" <yhs@fb.com>, "John Fastabend" <john.fastabend@gmail.com>, "KP Singh" <kpsingh@kernel.org>, "Stanislav Fomichev" <sdf@google.com>, "Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>, "Mykola Lysenko" <mykolal@fb.com>, "Manu Bretelle" <chantr4@gmail.com>, "Pu Lehui" <pulehui@huawei.com> Subject: Re: [PATCH bpf-next 2/5] riscv, bpf: Relax restrictions on Zbb instructions Date: Thu, 28 Mar 2024 22:07:23 +0000 [thread overview] Message-ID: <20240328-ferocity-repose-c554f75a676c@spud> (raw) In-Reply-To: <3ed9fe94-2610-41eb-8a00-a9f37fcf2b1a@app.fastmail.com> [-- Attachment #1: Type: text/plain, Size: 2946 bytes --] On Thu, Mar 28, 2024 at 03:34:31PM -0400, Stefan O'Rear wrote: > On Thu, Mar 28, 2024, at 8:49 AM, Pu Lehui wrote: > > From: Pu Lehui <pulehui@huawei.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. > > This doesn't make sense to me. It doesn't make sense to me either. Of course the hardware's capability to understand an instruction is independent of whether or not a toolchain is capable of actually emitting the instruction. > RISCV_ISA_ZBB is defined as: > > Adds support to dynamically detect the presence of the ZBB > extension (basic bit manipulation) and enable its usage. > > In other words, RISCV_ISA_ZBB=n should disable everything that attempts > to detect Zbb at runtime. It is mostly relevant for code size reduction, > which is relevant for BPF since if RISCV_ISA_ZBB=n all rvzbb_enabled() > checks can be constant-folded. > > If BPF needs to become an exception (why?), this should be mentioned in > Kconfig. And in the commit message. On one hand I think this could be a reasonable thing to do in bpf as it is acting as a jit here, and doesn't actually need the alternatives that we are using elsewhere to enable the optimisations nor the compiler support. On the other the intention of that kconfig option is to control optimisations like rvzbb_enabled() gates, so this is gonna need a proper justification as to As I said on IRC to you earlier, I think the Kconfig options here are in need of a bit of a spring cleaning - they should be modified to explain their individual purposes, be that enabling optimisations in the kernel or being required for userspace. I'll try to send a patch for that if I remember tomorrow. Thanks, Conor. > > Signed-off-by: Pu Lehui <pulehui@huawei.com> > > --- > > arch/riscv/net/bpf_jit.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h > > index 5fc374ed98ea..bcf109b88df5 100644 > > --- a/arch/riscv/net/bpf_jit.h > > +++ b/arch/riscv/net/bpf_jit.h > > @@ -20,7 +20,7 @@ static inline bool rvc_enabled(void) > > > > static inline bool rvzbb_enabled(void) > > { > > - return IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && > > riscv_has_extension_likely(RISCV_ISA_EXT_ZBB); > > + return riscv_has_extension_likely(RISCV_ISA_EXT_ZBB); > > } > > > > enum { > > -- > > 2.34.1 > > > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 228 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: Conor Dooley <conor@kernel.org> To: Stefan O'Rear <sorear@fastmail.com> Cc: "Pu Lehui" <pulehui@huaweicloud.com>, bpf@vger.kernel.org, linux-riscv@lists.infradead.org, netdev@vger.kernel.org, "Björn Töpel" <bjorn@kernel.org>, "Alexei Starovoitov" <ast@kernel.org>, "Daniel Borkmann" <daniel@iogearbox.net>, "Andrii Nakryiko" <andrii@kernel.org>, "Martin KaFai Lau" <martin.lau@linux.dev>, "Eduard Zingerman" <eddyz87@gmail.com>, "Song Liu" <song@kernel.org>, "Yonghong Song" <yhs@fb.com>, "John Fastabend" <john.fastabend@gmail.com>, "KP Singh" <kpsingh@kernel.org>, "Stanislav Fomichev" <sdf@google.com>, "Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>, "Mykola Lysenko" <mykolal@fb.com>, "Manu Bretelle" <chantr4@gmail.com>, "Pu Lehui" <pulehui@huawei.com> Subject: Re: [PATCH bpf-next 2/5] riscv, bpf: Relax restrictions on Zbb instructions Date: Thu, 28 Mar 2024 22:07:23 +0000 [thread overview] Message-ID: <20240328-ferocity-repose-c554f75a676c@spud> (raw) In-Reply-To: <3ed9fe94-2610-41eb-8a00-a9f37fcf2b1a@app.fastmail.com> [-- Attachment #1.1: Type: text/plain, Size: 2946 bytes --] On Thu, Mar 28, 2024 at 03:34:31PM -0400, Stefan O'Rear wrote: > On Thu, Mar 28, 2024, at 8:49 AM, Pu Lehui wrote: > > From: Pu Lehui <pulehui@huawei.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. > > This doesn't make sense to me. It doesn't make sense to me either. Of course the hardware's capability to understand an instruction is independent of whether or not a toolchain is capable of actually emitting the instruction. > RISCV_ISA_ZBB is defined as: > > Adds support to dynamically detect the presence of the ZBB > extension (basic bit manipulation) and enable its usage. > > In other words, RISCV_ISA_ZBB=n should disable everything that attempts > to detect Zbb at runtime. It is mostly relevant for code size reduction, > which is relevant for BPF since if RISCV_ISA_ZBB=n all rvzbb_enabled() > checks can be constant-folded. > > If BPF needs to become an exception (why?), this should be mentioned in > Kconfig. And in the commit message. On one hand I think this could be a reasonable thing to do in bpf as it is acting as a jit here, and doesn't actually need the alternatives that we are using elsewhere to enable the optimisations nor the compiler support. On the other the intention of that kconfig option is to control optimisations like rvzbb_enabled() gates, so this is gonna need a proper justification as to As I said on IRC to you earlier, I think the Kconfig options here are in need of a bit of a spring cleaning - they should be modified to explain their individual purposes, be that enabling optimisations in the kernel or being required for userspace. I'll try to send a patch for that if I remember tomorrow. Thanks, Conor. > > Signed-off-by: Pu Lehui <pulehui@huawei.com> > > --- > > arch/riscv/net/bpf_jit.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h > > index 5fc374ed98ea..bcf109b88df5 100644 > > --- a/arch/riscv/net/bpf_jit.h > > +++ b/arch/riscv/net/bpf_jit.h > > @@ -20,7 +20,7 @@ static inline bool rvc_enabled(void) > > > > static inline bool rvzbb_enabled(void) > > { > > - return IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && > > riscv_has_extension_likely(RISCV_ISA_EXT_ZBB); > > + return riscv_has_extension_likely(RISCV_ISA_EXT_ZBB); > > } > > > > enum { > > -- > > 2.34.1 > > > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv [-- Attachment #1.2: signature.asc --] [-- Type: application/pgp-signature, Size: 228 bytes --] [-- Attachment #2: Type: text/plain, Size: 161 bytes --] _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2024-03-28 22:07 UTC|newest] Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-03-28 12:49 [PATCH bpf-next 0/5] Support local vmtest for riscv64 Pu Lehui 2024-03-28 12:49 ` Pu Lehui 2024-03-28 12:49 ` [PATCH bpf-next 1/5] selftests/bpf: Enable cross platform testing for local vmtest Pu Lehui 2024-03-28 12:49 ` Pu Lehui 2024-03-28 12:49 ` [PATCH bpf-next 2/5] riscv, bpf: Relax restrictions on Zbb instructions Pu Lehui 2024-03-28 12:49 ` Pu Lehui 2024-03-28 19:34 ` Stefan O'Rear 2024-03-28 19:34 ` Stefan O'Rear 2024-03-28 22:07 ` Conor Dooley [this message] 2024-03-28 22:07 ` Conor Dooley 2024-03-29 10:05 ` Pu Lehui 2024-03-29 10:05 ` Pu Lehui 2024-04-02 14:25 ` Björn Töpel 2024-04-02 14:25 ` Björn Töpel 2024-04-02 17:38 ` Conor Dooley 2024-04-02 17:38 ` Conor Dooley 2024-04-02 19:00 ` Björn Töpel 2024-04-02 19:00 ` Björn Töpel 2024-04-03 1:20 ` Conor Dooley 2024-04-03 1:20 ` Conor Dooley 2024-04-03 10:05 ` Pu Lehui 2024-04-03 10:05 ` Pu Lehui 2024-04-03 12:29 ` Conor Dooley 2024-04-03 12:29 ` Conor Dooley 2024-03-29 11:23 ` Conor Dooley 2024-03-29 11:23 ` Conor Dooley 2024-03-30 10:19 ` Pu Lehui 2024-03-30 10:19 ` Pu Lehui 2024-03-30 10:19 ` Pu Lehui 2024-03-30 10:19 ` Pu Lehui 2024-03-31 17:49 ` Samuel Holland 2024-03-31 17:49 ` Samuel Holland 2024-04-02 14:18 ` Björn Töpel 2024-04-02 14:18 ` Björn Töpel 2024-04-02 14:27 ` Björn Töpel 2024-04-02 14:27 ` Björn Töpel 2024-04-02 16:03 ` Daniel Borkmann 2024-04-02 16:03 ` Daniel Borkmann 2024-04-03 10:19 ` Pu Lehui 2024-04-03 10:19 ` Pu Lehui 2024-03-28 12:49 ` [PATCH bpf-next 3/5] selftests/bpf: Add config.riscv64 Pu Lehui 2024-03-28 12:49 ` Pu Lehui 2024-03-28 12:49 ` [PATCH bpf-next 4/5] selftests/bpf: Add DENYLIST.riscv64 Pu Lehui 2024-03-28 12:49 ` Pu Lehui 2024-03-28 12:49 ` [PATCH bpf-next 5/5] selftests/bpf: Add riscv64 configurations to local vmtest Pu Lehui 2024-03-28 12:49 ` Pu Lehui 2024-03-29 9:08 ` [PATCH bpf-next 0/5] Support local vmtest for riscv64 Eduard Zingerman 2024-03-29 9:08 ` Eduard Zingerman 2024-03-29 10:10 ` Pu Lehui 2024-03-29 10:10 ` Pu Lehui 2024-03-29 19:46 ` Eduard Zingerman 2024-03-29 19:46 ` Eduard Zingerman 2024-03-30 10:12 ` Pu Lehui 2024-03-30 10:12 ` Pu Lehui 2024-03-30 10:12 ` Pu Lehui 2024-03-30 10:12 ` Pu Lehui 2024-04-02 23:40 ` Eduard Zingerman 2024-04-02 23:40 ` Eduard Zingerman 2024-04-03 10:31 ` Pu Lehui 2024-04-03 10:31 ` Pu Lehui
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