From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Daniel Borkmann" <daniel@iogearbox.net>, <puranjay@kernel.org>
Cc: <memxor@gmail.com>, <bpf@vger.kernel.org>
Subject: Re: [PATCH bpf-next 19/21] bpf, arm64: Split 24-bit immediates of add, sub and equality compares
Date: Wed, 28 Oct 2026 18:41:05 +0000 [thread overview]
Message-ID: <DMGOWPMN84X8.XMJMHFQ87RVI@gmail.com> (raw)
In-Reply-To: <20261027182445.1156335-20-daniel@iogearbox.net>
On Tue, Oct 27, 2026 at 11:24 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
> An add, sub or compare with an immediate that neither the plain nor the
> shifted 12-bit field takes moved the immediate into a register first,
> two moves for most immediates up to 24 bits and then the add. Take two
> adds or subs instead, of the upper 12 bits shifted and of the lower 12:
> an instruction fewer, at a cycle more on the path of the operand, as the
> two depend on each other where the moves did not, so an immediate that a
> single move produces keeps the move. A compare for equality takes the
> upper 12 bits off into a scratch register and compares against the lower
> 12, as the subtraction keeps equality.
[...]
> arch/arm64/net/bpf_jit_comp.c | 113 ++++++++++++++++++++++------------
> 1 file changed, 74 insertions(+), 39 deletions(-)
hmm Can we drop this patch?
It saves 4 bytes and adds a cycle of latency?
Doesn't seem worth it.
next prev parent reply other threads:[~2026-10-28 18:41 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-27 18:24 [PATCH bpf-next 00/21] bpf: Various arm64 BPF JIT improvements Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 01/21] bpf, arm64: Free the offset table of a subprog in bpf_jit_free Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 02/21] bpf, arm64: Free the private stack when a pass over the image fails Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 03/21] bpf, arm64: Emit ISB SY in the speculation barriers Daniel Borkmann
2026-10-28 13:29 ` Luis Gerhorst
2026-10-28 13:38 ` Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 04/21] arm64, insn: Reject sign extending loads of 64 bits Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 05/21] bpf, arm64: Keep the ll/sc atomics address apart from the old value Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 06/21] arm64, insn: Add the LDUR/STUR, UMULH/SMULH and TBZ/TBNZ encodings Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 07/21] bpf: Move the division magic number computation out of the x86 JIT Daniel Borkmann
2026-10-28 18:38 ` Alexei Starovoitov
2026-10-27 18:24 ` [PATCH bpf-next 08/21] bpf, arm64: Consolidate the load and store emission into a helper Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 09/21] bpf, arm64: Use the unscaled forms for negative and unaligned offsets Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 10/21] bpf, arm64: Store zero immediates from the zero register Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 11/21] bpf, arm64: Zero extend the arena offset in register offset accesses Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 12/21] bpf, arm64: Adjust compares with unencodable immediates by one Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 13/21] bpf, arm64: Materialize immediates with fewer instructions Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 14/21] bpf, arm64: Shorten the tail call sequence Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 15/21] bpf, arm64: Divide by constants via multiplication with a magic number Daniel Borkmann
2026-10-27 19:08 ` bot+bpf-ci
2026-10-27 18:24 ` [PATCH bpf-next 16/21] bpf, arm64: Use a move or mvn for the and and xor with all ones Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 17/21] bpf, arm64: Use cbz, cbnz, tbz and tbnz for zero, sign and bit tests Daniel Borkmann
2026-10-28 18:39 ` Alexei Starovoitov
2026-10-27 18:24 ` [PATCH bpf-next 18/21] bpf, arm64: Multiply by constants with shifts, adds and subs Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 19/21] bpf, arm64: Split 24-bit immediates of add, sub and equality compares Daniel Borkmann
2026-10-28 18:41 ` Alexei Starovoitov [this message]
2026-10-27 18:24 ` [PATCH bpf-next 20/21] selftests/bpf: Let the arm64 private stack check skip the BTI pad Daniel Borkmann
2026-10-27 18:24 ` [PATCH bpf-next 21/21] selftests/bpf: Extend the JIT instruction tests for arm64 encodings Daniel Borkmann
2026-10-27 19:08 ` bot+bpf-ci
2026-10-28 12:38 ` Daniel Borkmann
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