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 X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C052C433E0 for ; Thu, 9 Jul 2020 09:21:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16812206A1 for ; Thu, 9 Jul 2020 09:21:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="S0FIwz36" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726291AbgGIJVK (ORCPT ); Thu, 9 Jul 2020 05:21:10 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:26638 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726122AbgGIJVI (ORCPT ); Thu, 9 Jul 2020 05:21:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594286467; 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=fpT1tlU+FAIRvHikZIQn2nvVl9NUNq40o1v5G/MxGTw=; b=S0FIwz36oVS/P+UUik7Zoi+d3nBSYGS311tvJ3B49x4WS4NuQeF2Ka9xmBXfA027YEIrTE 2mZp7RGUyzwZgOIiY+qSbXpv5zvF2X6873SfFZYLmthbECJeu6Gp55cMm9z5hiHGvvM0rV yd3IcWGaMPYAk7aQmlKo36C76+AgNT4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-459-S4HiYPomPzuTzsOAv4VZxQ-1; Thu, 09 Jul 2020 05:21:03 -0400 X-MC-Unique: S4HiYPomPzuTzsOAv4VZxQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BA0AD107ACF7; Thu, 9 Jul 2020 09:21:01 +0000 (UTC) Received: from ovpn-113-239.ams2.redhat.com (ovpn-113-239.ams2.redhat.com [10.36.113.239]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7CA7F6106A; Thu, 9 Jul 2020 09:20:59 +0000 (UTC) Message-ID: <9dbb08f05890cc4130b54c80e4f4072b49d9f0ed.camel@redhat.com> Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc From: Paolo Abeni To: Cong Wang Cc: Josh Hunt , Jonas Bonn , Michael Zhivich , David Miller , John Fastabend , LKML , Linux Kernel Network Developers Date: Thu, 09 Jul 2020 11:20:58 +0200 In-Reply-To: References: <465a540e-5296-32e7-f6a6-79942dfe2618@netrounds.com> <20200623134259.8197-1-mzhivich@akamai.com> <1849b74f-163c-8cfa-baa5-f653159fefd4@akamai.com> <7fd86d97-6785-0b5f-1e95-92bc1da9df35@netrounds.com> <500b4843cb7c425ea5449fe199095edd5f7feb0c.camel@redhat.com> <25ca46e4-a8c1-1c88-d6a9-603289ff44c3@akamai.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.3 (3.36.3-1.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, 2020-07-08 at 13:16 -0700, Cong Wang wrote: > On Tue, Jul 7, 2020 at 7:18 AM Paolo Abeni wrote: > > So the regression with 2 pktgen threads is still relevant. 'perf' shows > > relevant time spent into net_tx_action() and __netif_schedule(). > > So, touching the __QDISC_STATE_SCHED bit in __dev_xmit_skb() is > not a good idea. > > Let me see if there is any other way to fix this. Thank you very much for the effort! I'm personally out of ideas for a real fix that would avoid regressions. To be more exaustive this are the sources of overhead, as far as I can observe them with perf: - contention on q->state, in __netif_schedule() - execution of net_tx_action() when there are no packet to be served Cheers, Paolo