From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754778Ab1JANEW (ORCPT ); Sat, 1 Oct 2011 09:04:22 -0400 Received: from casper.infradead.org ([85.118.1.10]:34090 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751339Ab1JANER convert rfc822-to-8bit (ORCPT ); Sat, 1 Oct 2011 09:04:17 -0400 Subject: Re: [RFC][PATCH 0/5] Signal scalability series From: Peter Zijlstra To: Matt Fleming Cc: Tejun Heo , Oleg Nesterov , linux-kernel@vger.kernel.org, Tony Luck , Thomas Gleixner Date: Sat, 01 Oct 2011 15:03:29 +0200 In-Reply-To: <1317464192.3375.57.camel@mfleming-mobl1.ger.corp.intel.com> References: <1317395577-14091-1-git-send-email-matt@console-pimps.org> <20110930165206.GA22048@redhat.com> <1317412823.3375.34.camel@mfleming-mobl1.ger.corp.intel.com> <20110930235625.GD2658@mtj.dyndns.org> <1317464192.3375.57.camel@mfleming-mobl1.ger.corp.intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1317474209.12973.15.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2011-10-01 at 11:16 +0100, Matt Fleming wrote: > I also think Thomas/Peter mentioned something about latency in > delivering timer signals because of contention on the per-process > siglock. They might have some more details on that. Right, so signal delivery is O(nr_threads), which precludes being able to deliver signals from hardirq context, leading to lots of ugly in -rt. The hope is that this work is a stepping stone to O(1) signal delivery. Breaking up the multitude of uses of siglock certainly seems worthwhile esp. if it also allows for a cleanup of the horrid mess called signal_struct (which really should be called process_struct or so). And yes, aside from that the siglock can be quite contended because its pretty much the one lock serializing all of the process wide state.