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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 774F7C64EB8 for ; Thu, 4 Oct 2018 09:37:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3AFD3213A2 for ; Thu, 4 Oct 2018 09:37:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3AFD3213A2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727829AbeJDQaK convert rfc822-to-8bit (ORCPT ); Thu, 4 Oct 2018 12:30:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49868 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727046AbeJDQaK (ORCPT ); Thu, 4 Oct 2018 12:30:10 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 50FF8C053FDE; Thu, 4 Oct 2018 09:37:45 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-149.rdu2.redhat.com [10.10.120.149]) by smtp.corp.redhat.com (Postfix) with ESMTP id EBEAF1710E; Thu, 4 Oct 2018 09:37:43 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <153859250219.15389.11970533498295122206.stgit@warthog.procyon.org.uk> To: Paolo Abeni Cc: dhowells@redhat.com, netdev@vger.kernel.org, linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] udp: Allow kernel service to avoid udp socket rx queue MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <26467.1538645863.1@warthog.procyon.org.uk> Content-Transfer-Encoding: 8BIT Date: Thu, 04 Oct 2018 10:37:43 +0100 Message-ID: <26468.1538645863@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Thu, 04 Oct 2018 09:37:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Abeni wrote: > > There's a problem somewhere skb_recv_udp() that doesn't decrease the > > sk_rmem_alloc counter when a packet is extracted from the receive queue by > > a kernel service. > > If this is the case, it's really bad and need an explicit fix. However > it looks like sk_rmem_alloc is reclaimed by skb_recv_udp(), as it ends- > up calling udp_rmem_release() on succesfull dequeue. It certainly *looks* like it should do that, but nonetheless, the tracepoint I put in shows it going up and up. I can try putting in a tracepoint by the subtraction, see what that shows. > > Further, there doesn't seem any point in having the socket buffer being > > added to the UDP socket's rx queue since the rxrpc's data_ready handler > > takes it straight back out again (more or less, there seem to be occasional > > hold ups there). > > I really would really try to avoid adding another indirect call in the > data-path, unless strictly needed (to avoid more RETPOLINE overhead for > all other use-case). If skipping altogether the enqueuing makes sense > (I guess so, mostily for performance reasons), I *think* you can use > the already existing encap_rcv hook, initializing it to the rxrpc input > function, and updating such function to pull the udp header and ev. > initializing the pktinfo, if needed. Please see e.g. l2tp usage. I looked at that, but it seems that a global conditional is required to enable it - presumably for performance reasons. I presume I would need to: (1) Allocate a new UDP_ENCAP_* flag. (2) Replicate at least some of the stuff that gets done between the check in udp_queue_rcv_skb() and the call of __udp_enqueue_schedule_skb() such as calling packet filtering. I'm not sure whether I need to call things like ipv4_pktinfo_prepare(), sock_rps_save_rxhash(), sk_mark_napi_id() or sk_incoming_cpu_update() - are they of necessity to the UDP socket? > > Putting in some tracepoints show a significant delay occurring between packets > > coming in and thence being delivered to rxrpc: > > > > -0 [001] ..s2 67.631844: net_rtl8169_napi_rx: enp3s0 skb=07db0a32 > > ... > > -0 [001] ..s4 68.292778: rxrpc_rx_packet: d5ce8d37:bdb93c60:00000002:09c7 00000006 00000000 02 20 ACK 660967981 skb=07db0a32 > > > > The "660967981" is the time difference in nanoseconds between the sk_buff > > timestamp and the current time. It seems to match the time elapsed between > > the two trace lines reasonably well. I've seen anything up to about 4s. > > Can you please provide more data? I can give you a whole trace if you like. > specifically can you please add: > * a perf probe in rxrpc_data_ready() just after skb_recv_udp() > reporting the sk->sk_rmem_alloc and skb->truesize > * a perf probe in __udp_enqueue_schedule_skb() just before the 'if > (rmem > sk->sk_rcvbuf)' test reporting again sk->sk_rmem_alloc, skb- > >truesize and sk->sk_rcvbuf > And then provide the perf record -g -e ... /perf script output? Can't this be done by putting tracepoints there instead? I don't know how to do the perf stuff. What can that get that can't be obtained with a tracepoint? Thanks, David