From owner-freebsd-net@freebsd.org Sun Mar 22 18:30:53 2020 Return-Path: Delivered-To: freebsd-net@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id DFC0D2690DB for ; Sun, 22 Mar 2020 18:30:53 +0000 (UTC) (envelope-from rysto32@gmail.com) Received: from mail-qv1-xf2e.google.com (mail-qv1-xf2e.google.com [IPv6:2607:f8b0:4864:20::f2e]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "GTS CA 1O1" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 48lmKn1Mbyz3G68 for ; Sun, 22 Mar 2020 18:30:52 +0000 (UTC) (envelope-from rysto32@gmail.com) Received: by mail-qv1-xf2e.google.com with SMTP id p19so3424183qve.0 for ; Sun, 22 Mar 2020 11:30:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=XkGzGGWKgH48cg5FNE9OsKJusIOnyXMXympjMyVyq9U=; b=E7LvBwO9Ny4V6pV4KenX7uPuhHNIuOlu91C+3TciiPMJFETLfmyuZP6cu6F5Ziv3tj sO+6/wGrKy9jUj/t06tnFJ7yn9Nlpav+wiwNQvaAP/M045Fc3CBEdez8LJzSunLlEBD9 zr54oBUhhef0m4hAwq1yfUsQ/yCPMRrSKoV4pLwksJ2lRyg0Yu56JDsA1Tp6XIbkf8Fh h6P048D2zKiI1dFjMkVD+okPFDJqpFc8oTNg9iTbJ/1DXh2al8DQ/QzJvVmo2GimO5un 2dQ5f+6INRkbVG8NGDQooBOLlrLwo8b8+2tT56+1OECERbdPKWM3FhQbg4RT+snN9jvw fuSA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=XkGzGGWKgH48cg5FNE9OsKJusIOnyXMXympjMyVyq9U=; b=n3YOdS1lJWOMpRW46gW2qvV1SYu/9tlL3r053MBVy3GKU09w8Wv7fie55yU+sBs7cq 07HpSL2s+AHuwzTYPorYi+b7yRktRqoLHdM3+EDOOO6fF5DEGXXHSpMMX7+ez9dF6iEB jxmNZOD37q6Vmyqm8spn3GxE+8ryP72C13eCehuo2VGf9Tg/0RQabZoDx0mGkKo7QFVY xuS+YQfGDrJi7hBXDzM86pPHEgIPp9Umh+kvqvcI/kykZl7ggJljMG6AHFXVTcWUxczC pk16jWeXdd2WOpvvC2fDS1E1gXn2maTdymSuvfsyD1qQNGuIdguVGG+tNmV3/nOGM5nn 23Pw== X-Gm-Message-State: ANhLgQ0KzjUlUjeg8sf+/FNGzr5TjbEt0XgT4Tro36NC/RojaZ2GGEDX Enu6dHxmeY9xkvnwhSkYu18Sn7HMLYRRj6l2cD7QxQ0q X-Google-Smtp-Source: ADFU+vvrCJZxTcsFGVbIjuU45JyXvxLtbXBgdHS28+xOfIPXEXPtNEP2qbYBLbLK4txStDNn5U/0S7vYn/TigwmQK3E= X-Received: by 2002:a0c:fd85:: with SMTP id p5mr1469705qvr.205.1584901851953; Sun, 22 Mar 2020 11:30:51 -0700 (PDT) MIME-Version: 1.0 From: Ryan Stone Date: Sun, 22 Mar 2020 14:30:41 -0400 Message-ID: Subject: Can net.iflib.min_tx_latency=0 introduce an unbounded amount of latency? To: freebsd-net Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 48lmKn1Mbyz3G68 X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=E7LvBwO9; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (mx1.freebsd.org: domain of rysto32@gmail.com designates 2607:f8b0:4864:20::f2e as permitted sender) smtp.mailfrom=rysto32@gmail.com X-Spamd-Result: default: False [-2.00 / 15.00]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; FROM_HAS_DN(0.00)[]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; FREEMAIL_FROM(0.00)[gmail.com]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-net@freebsd.org]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_ONE(0.00)[1]; IP_SCORE_FREEMAIL(0.00)[]; IP_SCORE(0.00)[ip: (-5.05), ipnet: 2607:f8b0::/32(-0.54), asn: 15169(-0.66), country: US(-0.05)]; TO_DN_ALL(0.00)[]; DKIM_TRACE(0.00)[gmail.com:+]; DMARC_POLICY_ALLOW(-0.50)[gmail.com,none]; RCVD_IN_DNSWL_NONE(0.00)[e.2.f.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.4.6.8.4.0.b.8.f.7.0.6.2.list.dnswl.org : 127.0.5.0]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; SUBJECT_ENDS_QUESTION(1.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; DWL_DNSWL_NONE(0.00)[gmail.com.dwl.dnswl.org : 127.0.5.0] X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 22 Mar 2020 18:30:54 -0000 I've been tracking down a bug at work that appears to be due to excessive latency introduced on the TX side of a TCP connection. In looking through the iflib code, I noticed the tunable net.iflib.min_tx_latency. My reading of the iflib code is that if a packet is enqueued to a tx ring but not posted (when min_tx_latency=0), then iflib can introduce an unbounded amount of latency if the ring is idle. Is my reading of the code correct?