From: Puranjay Mohan <puranjay@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@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 <yonghong.song@linux.dev>,
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>, Zi Shen Lim <zlim.lnx@gmail.com>,
Xu Kuohai <xukuohai@huawei.com>,
Florent Revest <revest@chromium.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v4 2/2] bpf, arm64: inline bpf_get_smp_processor_id() helper
Date: Tue, 30 Apr 2024 18:48:00 +0000 [thread overview]
Message-ID: <mb61pzfta1ycf.fsf@kernel.org> (raw)
In-Reply-To: <20240429131647.50165-3-puranjay@kernel.org>
Puranjay Mohan <puranjay@kernel.org> writes:
> As ARM64 JIT now implements BPF_MOV64_PERCPU_REG instruction, inline
> bpf_get_smp_processor_id().
>
> ARM64 uses the per-cpu variable cpu_number to store the cpu id.
While implementing this on the RISC-V JIT[1], I realized that reading the
cpu_number from the per-cpu variable is not the best way to do this on
arm64.
arm64 now has the cpu number in the thread_info and reading that would
be more efficient.
Implementation in this patch is emitting:
; int cpu = bpf_get_smp_processor_id();
mov x7, #0xffff8000ffffffff
movk x7, #0x8207, lsl #16
movk x7, #0x2008
mrs x10, tpidr_el1
add x7, x7, x10
ldr w7, [x7]
If we do this in the JIT like I did for RISC-V[1]
We can emit:
; int cpu = bpf_get_smp_processor_id();
mrs x10, sp_el0
ldr w7, [x10, #24]
This gives ~ 10% improvement on glob-arr-inc and hash-inc compared to
3-4 % which this patch is providing.
I will send v5 using this approach.
[1] https://lore.kernel.org/all/20240430175834.33152-3-puranjay@kernel.org/
> Here is how the BPF and ARM64 JITed assembly changes after this commit:
>
> BPF
> =====
> BEFORE AFTER
> -------- -------
>
> int cpu = bpf_get_smp_processor_id(); int cpu = bpf_get_smp_processor_id();
> (85) call bpf_get_smp_processor_id#229032 (18) r0 = 0xffff800082072008
> (bf) r0 = &(void __percpu *)(r0)
> (61) r0 = *(u32 *)(r0 +0)
>
> ARM64 JIT
> ===========
>
> BEFORE AFTER
> -------- -------
>
> int cpu = bpf_get_smp_processor_id(); int cpu = bpf_get_smp_processor_id();
> mov x10, #0xfffffffffffff4d0 mov x7, #0xffff8000ffffffff
> movk x10, #0x802b, lsl #16 movk x7, #0x8207, lsl #16
> movk x10, #0x8000, lsl #32 movk x7, #0x2008
> blr x10 mrs x10, tpidr_el1
> add x7, x0, #0x0 add x7, x7, x10
> ldr w7, [x7]
>
> Performance improvement using benchmark[1]
>
> BEFORE AFTER
> -------- -------
>
> glob-arr-inc : 23.817 ± 0.019M/s glob-arr-inc : 24.631 ± 0.027M/s [+ 3.41%]
> arr-inc : 23.253 ± 0.019M/s arr-inc : 23.742 ± 0.023M/s [+ 2.10%]
> hash-inc : 12.258 ± 0.010M/s hash-inc : 12.625 ± 0.004M/s [+ 3.00%]
>
> [1] https://github.com/anakryiko/linux/commit/8dec900975ef
Thanks,
Puranjay
prev parent reply other threads:[~2024-04-30 18:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-29 13:16 [PATCH bpf-next v4 0/2] bpf, arm64: Support per-cpu instruction Puranjay Mohan
2024-04-29 13:16 ` [PATCH bpf-next v4 1/2] arm64, bpf: add internal-only MOV instruction to resolve per-CPU addrs Puranjay Mohan
2024-04-29 13:16 ` [PATCH bpf-next v4 2/2] bpf, arm64: inline bpf_get_smp_processor_id() helper Puranjay Mohan
2024-04-30 18:48 ` Puranjay Mohan [this message]
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