From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8A0F32701DA for ; Tue, 30 Dec 2025 06:34:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767076464; cv=none; b=FeEOn9MfEhjPpMQF4hR9QCdSxbgdaXDtWGFz4IXJFPPVZiixARSXbjsrddzW4l/jdR25bTeZZzrIG7ApigSmrZIeOk/2Q3x1eE09VCU24FV83FNy4VEmznes7+ikCeFvZHKyPCIzExcGq0BCPAMFbZGRx1jLW996/QS6dUX/iDE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767076464; c=relaxed/simple; bh=TKf5w0jut+gvRqj6BQLzeYsFg54V7ELSxqaG5ayiiFg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=FxbblumXM0/T0kE/7Hl7pLJiCQegaeu3oZEW3OrGKVG1vuPWWw76F3ZmN/fSrk2F83sK9+q+PAw+N1+86fdQjblWKM7/x5T7U+F7/YKohfbpRjRt2aW0+Uv6jsuGqLj1ONSOKgnFqf9EzzK/uuAnucvIryWltEH3S3+y49j0GuE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=VI7ubRs+; arc=none smtp.client-ip=91.218.175.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="VI7ubRs+" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1767076449; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BX74wYtIpBX9oc/n3E/vw1MH9I5JUevUkmGZqt3oGsA=; b=VI7ubRs+kGjndsmCpBipo1hi9ZVFTsRJqpkzIROD9YikIlIFU22v9tV4RiyZRrWqAtjsss 7LZ19OssnkbYub3YkVtdYeLDnsc4PmBMP++lUgBxAWeacrLiaJev/nsqQPHiHDZyzW4aHU 5oE3su+ihQlJuN4ZF7HRsVw3od6kV6E= From: Menglong Dong To: Menglong Dong , ast@kernel.org, Eduard Zingerman Cc: davem@davemloft.net, dsahern@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, jiang.biao@linux.dev, x86@kernel.org, hpa@zytor.com, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next] bpf, x86: inline bpf_get_current_task() for x86_64 Date: Tue, 30 Dec 2025 14:33:53 +0800 Message-ID: <6448186.lOV4Wx5bFT@7940hx> In-Reply-To: <0f0bd124a42723acf87b427cc69356a0e4b1e339.camel@gmail.com> References: <20251225104459.204104-1-dongml2@chinatelecom.cn> <0f0bd124a42723acf87b427cc69356a0e4b1e339.camel@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" X-Migadu-Flow: FLOW_OUT On 2025/12/30 03:58 Eduard Zingerman write: > On Thu, 2025-12-25 at 18:44 +0800, Menglong Dong wrote: > > Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64 > > to obtain better performance. The instruction we use here is: > > > > 65 48 8B 04 25 [offset] // mov rax, gs:[offset] > > > > Not sure if there is any side effect here. > > > > Signed-off-by: Menglong Dong > > --- > > The change makes sense to me. > Could you please address the compilation error reported by kernel test robot? Yeah, I'll send a V2 later. > Could you please also add a tests case using __jited annotation like > in verifier_ldsx.c? OK, sounds nice. > > > arch/x86/net/bpf_jit_comp.c | 33 +++++++++++++++++++++++++++++++++ > > 1 file changed, 33 insertions(+) > > > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > > index b69dc7194e2c..7f38481816f0 100644 > > --- a/arch/x86/net/bpf_jit_comp.c > > +++ b/arch/x86/net/bpf_jit_comp.c > > @@ -1300,6 +1300,19 @@ static void emit_st_r12(u8 **pprog, u32 size, u32 dst_reg, int off, int imm) > > emit_st_index(pprog, size, dst_reg, X86_REG_R12, off, imm); > > } > > > > +static void emit_ldx_percpu_r0(u8 **pprog, const void __percpu *ptr) > > +{ > > + u8 *prog = *pprog; > > + > > + /* mov rax, gs:[offset] */ > > + EMIT2(0x65, 0x48); > > + EMIT2(0x8B, 0x04); > > + EMIT1(0x25); > > + EMIT((u32)(unsigned long)ptr, 4); > > + > > + *pprog = prog; > > +} > > + > > static int emit_atomic_rmw(u8 **pprog, u32 atomic_op, > > u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size) > > { > > @@ -2435,6 +2448,15 @@ st: if (is_imm8(insn->off)) > > case BPF_JMP | BPF_CALL: { > > u8 *ip = image + addrs[i - 1]; > > > > + if (insn->src_reg == 0 && (insn->imm == BPF_FUNC_get_current_task || > > + insn->imm == BPF_FUNC_get_current_task_btf)) { > > + if (IS_ENABLED(CONFIG_USE_X86_SEG_SUPPORT)) > > + emit_ldx_percpu_r0(&prog, &const_current_task); > > + else > > + emit_ldx_percpu_r0(&prog, ¤t_task); > > Nit: arch/x86/include/asm/current.h says that current_task and const_current_task are aliases. > In that case, why would we need two branches here? It's not need here. I were not familiar with the per-cpu variable before, and didn't realize it. And it seems that the gs register is only used in the CONFIG_USE_X86_SEG_SUPPORT case, which is the common case. So maybe we can support it for this case only. For the !CONFIG_USE_X86_SEG_SUPPORT case, let me do more analysis to see if we can support it easily. Thanks! Menglong Dong > > > + break; > > + } > > + > > func = (u8 *) __bpf_call_base + imm32; > > if (src_reg == BPF_PSEUDO_CALL && tail_call_reachable) { > > LOAD_TAIL_CALL_CNT_PTR(stack_depth); > > @@ -4067,3 +4089,14 @@ bool bpf_jit_supports_timed_may_goto(void) > > { > > return true; > > } > > + > > +bool bpf_jit_inlines_helper_call(s32 imm) > > +{ > > + switch (imm) { > > + case BPF_FUNC_get_current_task: > > + case BPF_FUNC_get_current_task_btf: > > + return true; > > + default: > > + return false; > > + } > > +} >