From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: ast@kernel.org, Daniel Borkmann <daniel@iogearbox.net>
Cc: netdev@vger.kernel.org, Sandipan Das <sandipan@linux.vnet.ibm.com>
Subject: Re: [PATCH bpf-next 01/13] bpf: xor of a/x in cbpf can be done
Date: Mon, 29 Jan 2018 00:28:57 +0530 [thread overview]
Message-ID: <1517165673.b6qwvzzvuf.naveen@linux.ibm.com> (raw)
In-Reply-To: <20180126223348.11250-2-daniel@iogearbox.net>
in 32 bit alu
Daniel Borkmann wrote:
> Very minor optimization; saves 1 byte per program in x86_64
> JIT in cBPF prologue.
... but increases program size by 4 bytes on ppc64 :(
In general, this is an area I've been wanting to spend some time on.
Powerpc doesn't have 32-bit sub-registers, so we need to emit an
additional instruction to clear the higher 32-bits for all 32-bit
operations. I need to look at the performance impact.
- Naveen
>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Alexei Starovoitov <ast@kernel.org>
> ---
> net/core/filter.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 18da42a..cba2f73 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -401,8 +401,8 @@ static int bpf_convert_filter(struct sock_filter *prog, int len,
> /* Classic BPF expects A and X to be reset first. These need
> * to be guaranteed to be the first two instructions.
> */
> - *new_insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_A, BPF_REG_A);
> - *new_insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_X, BPF_REG_X);
> + *new_insn++ = BPF_ALU32_REG(BPF_XOR, BPF_REG_A, BPF_REG_A);
> + *new_insn++ = BPF_ALU32_REG(BPF_XOR, BPF_REG_X, BPF_REG_X);
>
> /* All programs must keep CTX in callee saved BPF_REG_CTX.
> * In eBPF case it's done by the compiler, here we need to
> --
> 2.9.5
>
>
>
next prev parent reply other threads:[~2018-01-28 18:59 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-26 22:33 [PATCH bpf-next 00/13] BPF improvements and fixes Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 01/13] bpf: xor of a/x in cbpf can be done in 32 bit alu Daniel Borkmann
2018-01-28 18:58 ` Naveen N. Rao [this message]
2018-01-28 20:51 ` [PATCH bpf-next 01/13] bpf: xor of a/x in cbpf can be done Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 02/13] bpf: improve dead code sanitizing Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 03/13] bpf: make unknown opcode handling more robust Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 04/13] bpf: fix subprog verifier bypass by div/mod by 0 exception Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 05/13] bpf, x86_64: remove obsolete exception handling from div/mod Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 06/13] bpf, arm64: " Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 07/13] bpf, s390x: " Daniel Borkmann
2018-01-29 14:33 ` Michael Holzheu
2018-01-29 15:52 ` Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 08/13] bpf, ppc64: " Daniel Borkmann
2018-01-28 18:52 ` Naveen N. Rao
2018-01-26 22:33 ` [PATCH bpf-next 09/13] bpf, sparc64: " Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 10/13] bpf, mips64: " Daniel Borkmann
2018-01-26 22:39 ` David Daney
2018-01-26 22:33 ` [PATCH bpf-next 11/13] bpf, mips64: remove unneeded zero check from div/mod with k Daniel Borkmann
2018-01-26 22:36 ` David Daney
2018-01-26 22:33 ` [PATCH bpf-next 12/13] bpf, arm: remove obsolete exception handling from div/mod Daniel Borkmann
2018-01-26 22:33 ` [PATCH bpf-next 13/13] bpf: add further test cases around div/mod and others Daniel Borkmann
2018-01-27 0:48 ` [PATCH bpf-next 00/13] BPF improvements and fixes Alexei Starovoitov
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