From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C64A1C433F5 for ; Thu, 21 Apr 2022 02:37:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1383783AbiDUCka (ORCPT ); Wed, 20 Apr 2022 22:40:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbiDUCk3 (ORCPT ); Wed, 20 Apr 2022 22:40:29 -0400 Received: from mail-ej1-x62a.google.com (mail-ej1-x62a.google.com [IPv6:2a00:1450:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1725F2C4; Wed, 20 Apr 2022 19:37:41 -0700 (PDT) Received: by mail-ej1-x62a.google.com with SMTP id s18so7294163ejr.0; Wed, 20 Apr 2022 19:37:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=bc6AgyH0v562982pO2Yvqlt5tZo1Pxn0qGkmDxnDxTc=; b=NDZsv++7ZxmRwH9twfMYY1A+fEgP/rXvja7BsjUu2f+5jP0ByNXtXs2jGXNsMhavn4 oiFnnCQTxIqLtqqqmAsnkpAM1k/uJZwu9Pv7odDIITUjAlI8y7Vkqn/FGf5vVaIf06wk PmEwe7TiK2t/g30F/B4NK3VcHEF0EIcWhqSINZSfXlJkS3En6o96xsZpaLvo9R+rAfsH F8uGQ6E/EOEgoHUXaxuaeNFB2d3U2p0z7XEIgM0AJGDutrA82nFyyq+JOS83+ZCfesRn VqANgAQeFilKK6oHyBcIe9hn5QcG/wx+pPNok9Y7oZD4AFQXrtB1V4zsOEc1G/7DXtU+ g1Ng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=bc6AgyH0v562982pO2Yvqlt5tZo1Pxn0qGkmDxnDxTc=; b=5M7LtJc2QkfYnSwNJkfA6eY3K+ZeeVVAS4mkOO/DMKTrDseSZ08wqdUx7uu/ecXD4Z LjAuEdqsTLFdwaqFSfQNxsgIb59QVLBJU7+rbbe+0OjYDhOw20iZJkGWkrpX/BTxPiXF fMV5R25BH9RjjD85GCabVoNTQrGon7b9GXKZgkxk6vnsKx517gWzsIHBWBFuIEzwcE6S T8R+Y5y51FB3ItDCI8TUAUKnZN5OcufHmR9XkH4iTWrZGKjiiKsYilZahxLoHWj3lfIt Z2XbnH3qqNQR+eGleqyG2pFDVLKrax+F4iANoKViTkzgWRxl2XDTVboqAwYOvp8PInj9 5blw== X-Gm-Message-State: AOAM533chuznfMH1FxdtXPNlHcyWE09pCrS9KhEmk8IJ4Pe//CAI4YzQ O2uAdDNHQ+YJKpWyB7gWCI5/gDSyaexorqJhfXDie165hBmOoA== X-Google-Smtp-Source: ABdhPJwcPnziEwqWtahGs8Isz+W7mW/jNnh7EFWcj/w42t3+lmdcFmjK/Y1paTP3/P12gB0Qs1A8s3qzj3uOuHmR96g= X-Received: by 2002:a17:907:7204:b0:6e8:c1e9:49f7 with SMTP id dr4-20020a170907720400b006e8c1e949f7mr20971128ejc.251.1650508659624; Wed, 20 Apr 2022 19:37:39 -0700 (PDT) MIME-Version: 1.0 References: <20220420122307.5290-1-xiangxia.m.yue@gmail.com> <878rrzj4r6.fsf@toke.dk> In-Reply-To: From: Tonghao Zhang Date: Thu, 21 Apr 2022 10:37:03 +0800 Message-ID: Subject: Re: [net-next v1] bpf: add bpf_ktime_get_real_ns helper To: Andrii Nakryiko Cc: =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Networking , bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Jiri Olsa , Dave Marchevsky , Kuniyuki Iwashima , Joanne Koong , Geliang Tang , "David S. Miller" , Jakub Kicinski , Eric Dumazet Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Thu, Apr 21, 2022 at 12:17 AM Andrii Nakryiko wrote: > > On Wed, Apr 20, 2022 at 5:53 AM Toke H=C3=B8iland-J=C3=B8rgensen wrote: > > > > xiangxia.m.yue@gmail.com writes: > > > > > From: Tonghao Zhang > > > > > > This patch introduce a new bpf_ktime_get_real_ns helper, which may > > > help us to measure the skb latency in the ingress/forwarding path: > > > > > > HW/SW[1] -> ip_rcv/tcp_rcv_established -> tcp_recvmsg_locked/tcp_upda= te_recv_tstamps > > > > > > * Insert BPF kprobe into ip_rcv/tcp_rcv_established invoking this hel= per. > > > Then we can inspect how long time elapsed since HW/SW. > > > * If inserting BPF kprobe tcp_update_recv_tstamps invoked by tcp_recv= msg, > > > we can measure how much latency skb in tcp receive queue. The reaso= n for > > > this can be application fetch the TCP messages too late. > > > > Why not just use one of the existing ktime helpers and also add a BPF > > probe to set the initial timestamp instead of relying on skb->tstamp? > > > > You don't even need a BPF probe for this. See [0] for how retsnoop is > converting bpf_ktime_get_ns() into real time. > > [0] https://github.com/anakryiko/retsnoop/blob/master/src/retsnoop.c#L6= 49-L668 I try to calculate this offset too. But one case: If administrator manually or NTP changes the clock, we should calculate the offset. How do we know the changes, one solution is that inserting kprobe in tk_set_wall_to_mono() kernel function, and using perf_event to notify userspace. > > -Toke --=20 Best regards, Tonghao