From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 7860317993 for ; Tue, 22 Oct 2024 01:46:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729561598; cv=none; b=NndPbmLeiI0/PpYwou5Q/9U2yySX5ir+ol6SWZ+n58OR4p9VpThnSMj0s+3xh4K4m9eKc2m7IxRz3+oYbyvS5woijFgg9kgQTrAjhaJUo8ZFyn4PCiSp7IaCJ8Shrl/dN2t/aeh9OpLoy2TEo8Pe+zEWgB5Kc01V6B7N7TaYHww= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729561598; c=relaxed/simple; bh=AzE8fYotIum1oWdGLMn7crbHnaUEkMFZL232IOQeR7A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=G/WJgj86TblbUY8Pf4M2gPTJQjylVVUOq/15/UYZq4LHmmnv/ScCQQs6y2dCx4U3nXPLLCgNoklK7r1CduK201BniqRNfO4HypavnbjA0ce+sXyV78OjYqvoaKiNPAZMP02L3bDhetvwum/GqNsIq3bm+OZSS10JeGyGgZYBtok= 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=lgJOCrqb; arc=none smtp.client-ip=95.215.58.181 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="lgJOCrqb" Message-ID: <0f61509c-3a00-422a-90f3-89bdfbd20037@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1729561592; 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=0ry3br5BFbDWeH/Tp4jOgN3WpdVS73dULoPmS6fyRyg=; b=lgJOCrqbe9MJC+9r+bxiOg8aVyT18h+AXOk6d2zNQ/PH/0vZKpvqaIy+VLM0nwQ6NsmkXe 6+zcglJtfm2zJKT5rTQy6On4AaEfFwq3xmu+aFXv+oj/ndeVXsXZR4PzAbHk3Rv9C2mmLl dFhjhfAeRb3dsC3E7MYGrTjHCiYNI4o= Date: Tue, 22 Oct 2024 09:46:18 +0800 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-US To: Yonghong Song , 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: <87faf17b-51aa-487f-8d49-bf297a64ffa6@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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. Thanks, Leon