From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta0.migadu.com (out-186.mta0.migadu.com [91.218.175.186]) (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 CA3E61A0BDC for ; Wed, 9 Oct 2024 14:59:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728485995; cv=none; b=gWH6s7yPaEpremHfUDgxdG2/lXYORS3MbGgbNJ16Tf5gq0QG8Xd72P0LclQhNzF18O9rxHQ0lr8KzXDCyXl8W/BKUMmc40Hn89XY2pm0kWOp6H19mvTadQy+VqedpW32HyLDXY6o6nb0ibRpojXwx9WVzPiaTp4rf5ClmQ/kl7k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728485995; c=relaxed/simple; bh=qyjfsJwfA1UWxpCp+hU05yXxehld8pBC2ECh6pLqgn4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gNwMk9DslbS8enkZapK7svMTDNnpRG0S2JgLMkodfZe5OO4i6EUQFiiYxDGzacLoPRzGslGjNbV6UoW+iezdENoVWTj4aGsqWJGjxw/12ku9B5y5l3JDbvjHsm5tFYrnGXCfHBjQiKpbmWmPzHB3u8B09Ls09bU9M+TQev7mOUo= 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=ahjZLxT+; arc=none smtp.client-ip=91.218.175.186 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="ahjZLxT+" Message-ID: <662873cb-a897-464e-bdb3-edf01363c3b2@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1728485989; 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=aRwvrKIiasFpos0WTtiMfaYbqIxZ/meilCsw6pjSXtI=; b=ahjZLxT+zbUXkD8gLewZcfK3ubnjZg6WVBon0Ef06j+VLsiV6Np2uvl8YegvvRejtpljeD GAbMk1Z4I4Uv3WtucAosoa8BFCRx/PLAhtE2Wdhz6SNLAFS7EGhf3w2pPFVJVmgkjUvAkS ENruZci8GsjPwyW37h+VwLvOKbgXLAg= Date: Wed, 9 Oct 2024 15:59:44 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next 0/9] net-timestamp: bpf extension to equip applications transparently To: Jason Xing Cc: Willem de Bruijn , davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, dsahern@kernel.org, willemb@google.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, 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, bpf@vger.kernel.org, netdev@vger.kernel.org, Jason Xing References: <20241008095109.99918-1-kerneljasonxing@gmail.com> <67057d89796b_1a41992944c@willemb.c.googlers.com.notmuch> <6b10ed31-c53f-4f99-9c23-e1ba34aa0905@linux.dev> <9c5b405c-9b3d-4c1f-b278-303fe24c7926@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Vadim Fedorenko In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 09/10/2024 15:35, Jason Xing wrote: > On Wed, Oct 9, 2024 at 9:58 PM Vadim Fedorenko > wrote: >> >> On 09/10/2024 14:47, Jason Xing wrote: >>> On Wed, Oct 9, 2024 at 9:16 PM Vadim Fedorenko >>> wrote: >>>> >>>> On 09/10/2024 12:48, Jason Xing wrote: >>>>> On Wed, Oct 9, 2024 at 7:12 PM Jason Xing wrote: >>>>>> >>>>>> On Wed, Oct 9, 2024 at 5:28 PM Vadim Fedorenko >>>>>> wrote: >>>>>>> >>>>>>> On 09/10/2024 02:05, Jason Xing wrote: >>>>>>>> On Wed, Oct 9, 2024 at 7:22 AM Jason Xing wrote: >>>>>>>>> >>>>>>>>> On Wed, Oct 9, 2024 at 2:44 AM Willem de Bruijn >>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> Jason Xing wrote: >>>>>>>>>>> From: Jason Xing >>>>>>>>>>> >>>>>>>>>>> A few weeks ago, I planned to extend SO_TIMESTMAMPING feature by using >>>>>>>>>>> tracepoint to print information (say, tstamp) so that we can >>>>>>>>>>> transparently equip applications with this feature and require no >>>>>>>>>>> modification in user side. >>>>>>>>>>> >>>>>>>>>>> Later, we discussed at netconf and agreed that we can use bpf for better >>>>>>>>>>> extension, which is mainly suggested by John Fastabend and Willem de >>>>>>>>>>> Bruijn. Many thanks here! So I post this series to see if we have a >>>>>>>>>>> better solution to extend. >>>>>>>>>>> >>>>>>>>>>> This approach relies on existing SO_TIMESTAMPING feature, for tx path, >>>>>>>>>>> users only needs to pass certain flags through bpf program to make sure >>>>>>>>>>> the last skb from each sendmsg() has timestamp related controlled flag. >>>>>>>>>>> For rx path, we have to use bpf_setsockopt() to set the sk->sk_tsflags >>>>>>>>>>> and wait for the moment when recvmsg() is called. >>>>>>>>>> >>>>>>>>>> As you mention, overall I am very supportive of having a way to add >>>>>>>>>> timestamping by adminstrators, without having to rebuild applications. >>>>>>>>>> BPF hooks seem to be the right place for this. >>>>>>>>>> >>>>>>>>>> There is existing kprobe/kretprobe/kfunc support. Supporting >>>>>>>>>> SO_TIMESTAMPING directly may be useful due to its targeted feature >>>>>>>>>> set, and correlation between measurements for the same data in the >>>>>>>>>> stream. >>>>>>>>>> >>>>>>>>>>> After this series, we could step by step implement more advanced >>>>>>>>>>> functions/flags already in SO_TIMESTAMPING feature for bpf extension. >>>>>>>>>> >>>>>>>>>> My main implementation concern is where this API overlaps with the >>>>>>>>>> existing user API, and how they might conflict. A few questions in the >>>>>>>>>> patches. >>>>>>>>> >>>>>>>>> Agreed. That's also what I'm concerned about. So I decided to ask for >>>>>>>>> related experts' help. >>>>>>>>> >>>>>>>>> How to deal with it without interfering with the existing apps in the >>>>>>>>> right way is the key problem. >>>>>>>> >>>>>>>> What I try to implement is let the bpf program have the highest >>>>>>>> precedence. It's similar to RTO min, see the commit as an example: >>>>>>>> >>>>>>>> commit f086edef71be7174a16c1ed67ac65a085cda28b1 >>>>>>>> Author: Kevin Yang >>>>>>>> Date: Mon Jun 3 21:30:54 2024 +0000 >>>>>>>> >>>>>>>> tcp: add sysctl_tcp_rto_min_us >>>>>>>> >>>>>>>> Adding a sysctl knob to allow user to specify a default >>>>>>>> rto_min at socket init time, other than using the hard >>>>>>>> coded 200ms default rto_min. >>>>>>>> >>>>>>>> Note that the rto_min route option has the highest precedence >>>>>>>> for configuring this setting, followed by the TCP_BPF_RTO_MIN >>>>>>>> socket option, followed by the tcp_rto_min_us sysctl. >>>>>>>> >>>>>>>> It includes three cases, 1) route option, 2) bpf option, 3) sysctl. >>>>>>>> The first priority can override others. It doesn't have a good >>>>>>>> chance/point to restore the icsk_rto_min field if users want to >>>>>>>> shutdown the bpf program because it is set in >>>>>>>> bpf_sol_tcp_setsockopt(). >>>>>>> >>>>>>> rto_min example is slightly different. With tcp_rto_min the doesn't >>>>>>> expect any data to come back to user space while for timestamping the >>>>>>> app may be confused directly by providing more data, or by not providing >>>>>>> expected data. I believe some hint about requestor of the data is needed >>>>>>> here. It will also help to solve the problem of populating sk_err_queue >>>>>>> mentioned by Martin. >>>>>> >>>>>> Sorry, I don't fully get it. In this patch series, this bpf extension >>>>>> feature will not rely on sk_err_queue any more to report tx timestamps >>>>>> to userspace. Bpf program can do that printing. >>>>>> >>>>>> Do you mean that it could be wrong if one skb carries the tsflags that >>>>>> are previously set due to the bpf program and then suddenly users >>>>>> detach the program? It indeed will put a new/cloned skb into the error >>>>>> queue. Interesting corner case. It seems I have to re-implement a >>>>>> totally independent tsflags for bpf extension feature. Do you have a >>>>>> better idea on this? >>>>> >>>>> I feel that if I could introduce bpf new flags like >>>>> SOF_TIMESTAMPING_TX_ACK_BPF for the last skb based on this patch >>>>> series, then it will not populate skb in sk_err_queue even users >>>>> remove the bpf program all of sudden. With this kind of specific bpf >>>>> flags, we can also avoid conflicting with the apps using >>>>> SO_TIEMSTAMPING feature. Let me give it a shot unless a better >>>>> solution shows up. >>>> >>>> It doesn't look great to have duplicate flags just to indicate that this >>>> particular timestamp was asked by a bpf program, even though it looks >>> >>> Or introduce a new field in struct sock or struct sk_buff so that >>> existing SOF_TIMESTAMPING_* can be reused. >> >> Well, I was thinking about this way. We can potentially add an array of >> tsflags meaning the index of the array is the requestor. That will be >> more flexible in terms of adding new requestor (like scheduler or >> congestion control algo) if needed. But it comes with increased memory >> usage on hot path which might be a blocker. > > Is the following code snippet what you expect? But I wonder why not > just add a u32 field instead and then use each bit of it defined in > include/uapi/linux/net_tstamp.h? > > diff --git a/include/net/sock.h b/include/net/sock.h > index b32f1424ecc5..4677f53da75a 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -445,6 +445,7 @@ struct sock { > u32 sk_reserved_mem; > int sk_forward_alloc; > u32 sk_tsflags; > + u32 new_tsflags[10]; > __cacheline_group_end(sock_write_rxtx); > > __cacheline_group_begin(sock_write_tx); > > I could be missing something. Sorry. If possible, could you show me > some code snippets? > > As for the new requestor, IIUC, do you want to add more tx timestamp > generating points in the future? It's more like this: diff --git a/include/net/sock.h b/include/net/sock.h index c58ca8dd561b..93f931dcc4cc 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -234,6 +234,14 @@ struct sock_common { struct bpf_local_storage; struct sk_filter; +enum { + SOCKETOPT_TS_REQUESTOR = 0, + CMSG_TS_REQUESTOR, + BPFPROG_TS_REQUESTOR, + + __MAX_TS_REQUESTOR, +}; + /** * struct sock - network layer representation of sockets * @__sk_common: shared layout with inet_timewait_sock @@ -444,7 +452,7 @@ struct sock { socket_lock_t sk_lock; u32 sk_reserved_mem; int sk_forward_alloc; - u32 sk_tsflags; + u32 sk_tsflags[__MAX_TS_REQUESTOR]; __cacheline_group_end(sock_write_rxtx); __cacheline_group_begin(sock_write_tx); And use existing SOF_TIMESTAMPING_* for each element in the array. Not sure that struct sock is the best place though, as some timestamping requests may be on per-packet basis for protocols other than TCP. Again, I'm just thinking out loud, kinda wild idea.