From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (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 508844D8AD for ; Thu, 24 Oct 2024 02:30:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729737012; cv=none; b=Mo13BG6fWJqDdcDjvBj5MW1DW5Oc5CKLTb8UEq++tdLW+4TXyBfg7I9OSRXzurV8c5dOFdm1eLmZNXP6bKtyZ6WzWEVWruDJrvn3weJXNSjJkWVCDBUOf1jR6p4Q/bydF4Y2qH5r3zo0Y38tg/Z/cgyqRn0L7VG+JVSrgs6eeLs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729737012; c=relaxed/simple; bh=XHXnwjR/WT7ydEEXZs+EfOs9PB2MAuypJFtPdr9jJr0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WJuhdBXEL+oRXf5KLYK7QgsIh9t9h53OKsQ1eTyJywRHF9ZSV1IsdBDCLSAEif/vSF7hE9RyHbcZkYJ1goN80BHgEikZmzmX6zCQIEUXeg4pHvdgbUfkZ9WXD9a9b07Wbaux8chTYvdhY6+QNLy7MJgb2O7/mFHldeOpwHroAoE= 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=gl+E8PRf; arc=none smtp.client-ip=91.218.175.179 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="gl+E8PRf" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729737006; 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=QxhphihRF1EDPTEf2N7U+4VuQPmCsu2iKoZXeY5taBc=; b=gl+E8PRfbQJDGy7RINgM1l0Ah/W6MzGQjFoEgDaDy/SCbkhrW2JS0zQwU++WCzv6+c86pF AyQsLv99xy5WX6cECgMhzC5Rw+H+zh9SRpLaT7/WOA8fhSupCL8uZtVLr35/Qp4pmjoTW9 bOzTVFZg2CkgPsbxvZcZMzx2Fz8Hi0w= Date: Wed, 23 Oct 2024 19:29:57 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next 1/2] bpf, x64: Propagate tailcall info only for tail_call_reachable subprogs Content-Language: en-GB To: Leon Hwang , bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, jolsa@kernel.org, eddyz87@gmail.com, kernel-patches-bot@fb.com References: <20241021133929.67782-1-leon.hwang@linux.dev> <20241021133929.67782-2-leon.hwang@linux.dev> <87faf17b-51aa-487f-8d49-bf297a64ffa6@linux.dev> <0f61509c-3a00-422a-90f3-89bdfbd20037@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <0f61509c-3a00-422a-90f3-89bdfbd20037@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 10/21/24 6:46 PM, Leon Hwang wrote: > > On 22/10/24 01:49, Yonghong Song wrote: >> On 10/21/24 6:39 AM, Leon Hwang wrote: >>> In the x86_64 JIT, when calling a function, tailcall info is >>> propagated if >>> the program is tail_call_reachable, regardless of whether the function >>> is a >>> subprog, helper, or kfunc. However, this propagation is unnecessary for >>> not-tail_call_reachable subprogs, helpers, or kfuncs. >>> >>> The verifier can determine if a subprog is tail_call_reachable. >>> Therefore, >>> it can be optimized to only propagate tailcall info when the callee is >>> subprog and the subprog is actually tail_call_reachable. >>> >>> Signed-off-by: Leon Hwang >>> --- >>>   arch/x86/net/bpf_jit_comp.c | 4 +++- >>>   kernel/bpf/verifier.c       | 6 ++++++ >>>   2 files changed, 9 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c >>> index 06b080b61aa57..6ad6886ecfc88 100644 >>> --- a/arch/x86/net/bpf_jit_comp.c >>> +++ b/arch/x86/net/bpf_jit_comp.c >>> @@ -2124,10 +2124,12 @@ st:            if (is_imm8(insn->off)) >>>                 /* call */ >>>           case BPF_JMP | BPF_CALL: { >>> +            bool pseudo_call = src_reg == BPF_PSEUDO_CALL; >>> +            bool subprog_tail_call_reachable = dst_reg; >>>               u8 *ip = image + addrs[i - 1]; >>>                 func = (u8 *) __bpf_call_base + imm32; >>> -            if (tail_call_reachable) { >>> +            if (pseudo_call && subprog_tail_call_reachable) { >> Why we need subprog_tail_call_reachable? Does >>     tail_call_reachable && psueudo_call >> work the same way? >> > 'tail_call_reachable && pseudo_call' works too. However, it will > propagate tailcall info to subprog even if the subprog is not > tail_call_reachable. > > subprog_tail_call_reachable indicates the subprog requires tailcall info > from its caller. > So, 'pseudo_call && subprog_tail_call_reachable' is better. In verifier.c, we have func[i]->aux->tail_call_reachable = env->subprog_info[i].tail_call_reachable; that is subprog_info tail_call_reachable has been transferred to func[i] tail_call_reachable. In x86 do_jit() func, we have bool tail_call_reachable = bpf_prog->aux->tail_call_reachable So looks like we do not need verifier.c change here. Did I miss anything? Could you give a concrete example to show subprog_tail_call_reachable approach is better than tail_call_reachable? > > Thanks, > Leon >