From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 DE05BDF60 for ; Thu, 6 Feb 2025 00:47:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738802839; cv=none; b=ZisKUEhZvP0g2R+SdNcf8ATqasISeKW822Mw+vdFcuK9u4KTi6U3yuDFPmZmWaxpBG1UUams0yesQR1CfmcGoxfTrgTHJlyaQJEVy1p9VIPtsoCMOU83r9mu01wcdQHN1yfQvZ4bqMO/G6v2ryn+qSnYHwYN9fgl9xdRCaB8W8U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738802839; c=relaxed/simple; bh=VxQjeGbQQN+KvByPtNpdah6SCaateHxALZrLBUN8hgI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qpARctB19/M9SYQk+Ek7XGg9FVwudvlXHJE6cWNMF2TQXf8g8HsbGuR9+kXxCQA7nBVFI25FaQ80UBWYU+fn04ql5TH8wDXdd2QvhAhs+fnC8NomKbitWoktLbiZa8L2WHVgf7x5pYzfxY5IdHiGPCyVhHUk5j42crZDqzu+PPE= 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=YDFA6ljx; arc=none smtp.client-ip=95.215.58.174 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="YDFA6ljx" Message-ID: <0a8e7b84-bab6-4852-8616-577d9b561f4c@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1738802833; 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=GUFWFmqMR+h08Bo4fFsn/LKp8dHIbel6tFLRIU+gSS4=; b=YDFA6ljxAKn2JgWNs1yj/UPBnA8gUq9DbSZjuA79P1g6twiAcUzNG8bFGOLgvlgO1CmAlV KacMGlirODRwISqPlo1lvsO+rrIo4TmsNFlpeeUU/9thTl5H8aj4wxvK2pBDv7lYCUQvsn obnheSQmKcvSvtVtq8VJGumVYXnZBZA= Date: Wed, 5 Feb 2025 16:47:04 -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 v8 10/12] bpf: make TCP tx timestamp bpf extension work To: Jason Xing Cc: Jakub Kicinski , davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, dsahern@kernel.org, willemdebruijn.kernel@gmail.com, willemb@google.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, horms@kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org References: <20250204183024.87508-1-kerneljasonxing@gmail.com> <20250204183024.87508-11-kerneljasonxing@gmail.com> <20250204175744.3f92c33e@kernel.org> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2/5/25 4:12 PM, Jason Xing wrote: > On Thu, Feb 6, 2025 at 5:57 AM Martin KaFai Lau wrote: >> >> On 2/4/25 5:57 PM, Jakub Kicinski wrote: >>> On Wed, 5 Feb 2025 02:30:22 +0800 Jason Xing wrote: >>>> + if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) && >>>> + SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING) && skb) { >>>> + struct skb_shared_info *shinfo = skb_shinfo(skb); >>>> + struct tcp_skb_cb *tcb = TCP_SKB_CB(skb); >>>> + >>>> + tcb->txstamp_ack_bpf = 1; >>>> + shinfo->tx_flags |= SKBTX_BPF; >>>> + shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1; >>>> + } >>> >>> If BPF program is attached we'll timestamp all skbs? Am I reading this >>> right? >> >> If the attached bpf program explicitly turns on the SK_BPF_CB_TX_TIMESTAMPING >> bit of a sock, then all skbs of this sock will be tx timestamp-ed. > > Martin, I'm afraid it's not like what you expect. Only the last > portion of the sendmsg will enter the above function which means if > the size of sendmsg is large, only the last skb will be set SKBTX_BPF > and be timestamped. Sure. The last skb of a large msg and more skb of small msg (or MSG_EOR). My point is, only attaching a bpf alone is not enough. The SK_BPF_CB_TX_TIMESTAMPING still needs to be turned on. > >> >>> >>> Wouldn't it be better to let BPF_SOCK_OPS_TS_SND_CB return whether it's >>> interested in tracing current packet all the way thru the stack? >> >> I like this idea. It can give the BPF prog a chance to do skb sampling on a >> particular socket. >> >> The return value of BPF_SOCK_OPS_TS_SND_CB (or any cgroup BPF prog return value) >> already has another usage, which its return value is currently enforced by the >> verifier. It is better not to convolute it further. >> >> I don't prefer to add more use cases to skops->reply either, which is an union >> of args[4], such that later progs (in the cgrp prog array) may lose the args value. >> >> Jason, instead of always setting SKBTX_BPF and txstamp_ack_bpf in the kernel, a >> new BPF kfunc can be added so that the BPF prog can call it to selectively set >> SKBTX_BPF and txstamp_ack_bpf in some skb. > > Agreed because at netdev 0x19 I have an explicit plan to share the > experience from our company about how to trace all the skbs which were > completed through a kernel module. It's how we use in production > especially for debug or diagnose use. This is fine. The bpf prog can still do that by calling the kfunc. I don't see why move the bit setting into kfunc makes the whole set won't work. > I'm not knowledgeable enough about BPF, so I'd like to know if there > are some functions that I can take as good examples? > > I think it's a standalone and good feature, can I handle it after this series? Unfortunately, no. Once the default is on, this cannot be changed. I think Jakub's suggestion to allow bpf prog selectively choose skb to timestamp is useful, so I suggested a way to do it.