linux-kernel - Re: [PATCH bpf-next v3 09/14] bpf: Pull out a macro for interpreting atomic ALU operations

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Date:   Thu, 3 Dec 2020 22:30:18 -0800
From:   Yonghong Song <yhs@...com>
To:     Brendan Jackman <jackmanb@...gle.com>, <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        <linux-kernel@...r.kernel.org>, Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH bpf-next v3 09/14] bpf: Pull out a macro for interpreting
 atomic ALU operations



On 12/3/20 8:02 AM, Brendan Jackman wrote:
> Since the atomic operations that are added in subsequent commits are
> all isomorphic with BPF_ADD, pull out a macro to avoid the
> interpreter becoming dominated by lines of atomic-related code.
> 
> Note that this sacrificies interpreter performance (combining
> STX_ATOMIC_W and STX_ATOMIC_DW into single switch case means that we
> need an extra conditional branch to differentiate them) in favour of
> compact and (relatively!) simple C code.
> 
> Change-Id: I8cae5b66e75f34393de6063b91c05a8006fdd9e6
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>

Ack with a minor suggestion below.

Acked-by: Yonghong Song <yhs@...com>

> ---
>   kernel/bpf/core.c | 79 +++++++++++++++++++++++------------------------
>   1 file changed, 38 insertions(+), 41 deletions(-)
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 28f960bc2e30..498d3f067be7 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1618,55 +1618,52 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
>   	LDX_PROBE(DW, 8)
>   #undef LDX_PROBE
>   
> -	STX_ATOMIC_W:
> -		switch (IMM) {
> -		case BPF_ADD:
> -			/* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
> -			atomic_add((u32) SRC, (atomic_t *)(unsigned long)
> -				   (DST + insn->off));
> -			break;
> -		case BPF_ADD | BPF_FETCH:
> -			SRC = (u32) atomic_fetch_add(
> -				(u32) SRC,
> -				(atomic_t *)(unsigned long) (DST + insn->off));
> -			break;
> -		case BPF_XCHG:
> -			SRC = (u32) atomic_xchg(
> -				(atomic_t *)(unsigned long) (DST + insn->off),
> -				(u32) SRC);
> -			break;
> -		case BPF_CMPXCHG:
> -			BPF_R0 = (u32) atomic_cmpxchg(
> -				(atomic_t *)(unsigned long) (DST + insn->off),
> -				(u32) BPF_R0, (u32) SRC);
> +#define ATOMIC(BOP, KOP)						\

ATOMIC a little bit generic. Maybe ATOMIC_FETCH_BOP?

> +		case BOP:						\
> +			if (BPF_SIZE(insn->code) == BPF_W)		\
> +				atomic_##KOP((u32) SRC, (atomic_t *)(unsigned long) \
> +					     (DST + insn->off));	\
> +			else						\
> +				atomic64_##KOP((u64) SRC, (atomic64_t *)(unsigned long) \
> +					       (DST + insn->off));	\
> +			break;						\
> +		case BOP | BPF_FETCH:					\
> +			if (BPF_SIZE(insn->code) == BPF_W)		\
> +				SRC = (u32) atomic_fetch_##KOP(		\
> +					(u32) SRC,			\
> +					(atomic_t *)(unsigned long) (DST + insn->off)); \
> +			else						\
> +				SRC = (u64) atomic64_fetch_##KOP(	\
> +					(u64) SRC,			\
> +					(atomic64_t *)(s64) (DST + insn->off)); \
>   			break;
> -		default:
> -			goto default_label;
> -		}
> -		CONT;
>   
>   	STX_ATOMIC_DW:
> +	STX_ATOMIC_W:
>   		switch (IMM) {
> -		case BPF_ADD:
> -			/* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
> -			atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
> -				     (DST + insn->off));
> -			break;
> -		case BPF_ADD | BPF_FETCH:
> -			SRC = (u64) atomic64_fetch_add(
> -				(u64) SRC,
> -				(atomic64_t *)(s64) (DST + insn->off));
> -			break;
> +		ATOMIC(BPF_ADD, add)
> +
>   		case BPF_XCHG:
> -			SRC = (u64) atomic64_xchg(
> -				(atomic64_t *)(u64) (DST + insn->off),
> -				(u64) SRC);
> +			if (BPF_SIZE(insn->code) == BPF_W)
> +				SRC = (u32) atomic_xchg(
> +					(atomic_t *)(unsigned long) (DST + insn->off),
> +					(u32) SRC);
> +			else
> +				SRC = (u64) atomic64_xchg(
> +					(atomic64_t *)(u64) (DST + insn->off),
> +					(u64) SRC);
>   			break;
>   		case BPF_CMPXCHG:
> -			BPF_R0 = (u64) atomic64_cmpxchg(
> -				(atomic64_t *)(u64) (DST + insn->off),
> -				(u64) BPF_R0, (u64) SRC);
> +			if (BPF_SIZE(insn->code) == BPF_W)
> +				BPF_R0 = (u32) atomic_cmpxchg(
> +					(atomic_t *)(unsigned long) (DST + insn->off),
> +					(u32) BPF_R0, (u32) SRC);
> +			else
> +				BPF_R0 = (u64) atomic64_cmpxchg(
> +					(atomic64_t *)(u64) (DST + insn->off),
> +					(u64) BPF_R0, (u64) SRC);
>   			break;
> +
>   		default:
>   			goto default_label;
>   		}
>