Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754414AbbHFP2B (ORCPT ); Thu, 6 Aug 2015 11:28:01 -0400 Received: from mail-lb0-f173.google.com ([209.85.217.173]:34588 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753548AbbHFP17 (ORCPT ); Thu, 6 Aug 2015 11:27:59 -0400 MIME-Version: 1.0 In-Reply-To: <55C30769.9090509@zonque.org> References: <55C30769.9090509@zonque.org> From: Andy Lutomirski Date: Thu, 6 Aug 2015 08:27:38 -0700 Message-ID: Subject: Re: kdbus: to merge or not to merge? To: Daniel Mack Cc: David Herrmann , Linus Torvalds , Andy Lutomirski , "linux-kernel@vger.kernel.org" , Djalal Harouni , Greg KH , Havoc Pennington , "Eric W. Biederman" , One Thousand Gnomes , Tom Gundersen , "Kalle A. Sandstrom" , Borislav Petkov , cee1 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2511 Lines: 52 On Thu, Aug 6, 2015 at 12:06 AM, Daniel Mack wrote: > Hi Andy, > > On 08/05/2015 02:18 AM, Andy Lutomirski wrote: >> I added the missing sd_bus_unref call. >> >> With userspace dbus, my program takes 95% CPU and dbus-daemon takes >> 88% CPU or so. >> >> With kdbus, I see abuse-bus (my test), systemd-journald, >> systemd-bus-proxy, auditd, gnome-shell, mission-control, sedispatch, >> firewalld, polkitd, NetworkManager, systemd, avahi-daemon, audisp, >> abrt-dump-jour* (whatever it's called -- it truncated), upowerd, and >> systemd-logind all taking tons of CPU. I've listed them in decreasing >> order of amount of CPU burned -- the top several are taking about as >> much as is possible. Load average is over 13. That's if I run it >> from a text console while I'm logged in to gnome in a different VT. > > That's right, I can reproduce this here. To explain what's going on, let > me provide some background. > > Every time a client connects to kdbus, a new ID is assigned to the > connection, and other connections which have previously subscribed to > notifications of type KDBUS_ITEM_ID_ADD or _REMOVE get a notification > and are woken up so they can dispatch it. By default, no such matches > exists, applicaions have to explicitly opt-in if they are interested in > these events. > > In DBus (both kdbus and DBus1), such matches are installed on the > NameOwnerChanged signal, and they can be either specific to a single ID, > or broad, which will make them match on any ID. There's actually no > reason for applications to install unspecific matches, but if they do, > they will of course get what they asked for, and are woken up on every > ID that is added to or removed from the bus. What you're seeing in your > system profile is that some applications misbehave and install > unspecific matches when they shouldn't. That's a userspace bug that > needs fixing. Two candidates were actually in the systemd code base > (logind and PID1), and both are now patched. Can you point me at the patch? It sounds like that will reduce the scalability issue with this particular test from whatever userspace overhead exists * number of clients to just the overhead of looping over all clients and their matches in the kernel. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/