From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756072AbYECWFc (ORCPT ); Sat, 3 May 2008 18:05:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754526AbYECWFY (ORCPT ); Sat, 3 May 2008 18:05:24 -0400 Received: from victor.provo.novell.com ([137.65.250.26]:51309 "EHLO victor.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754315AbYECWFX (ORCPT ); Sat, 3 May 2008 18:05:23 -0400 Subject: Re: preempt-rt, need old style rwlocks for systemtap From: "Peter W. Morreale" To: "Frank Ch. Eigler" Cc: Clark Williams , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org In-Reply-To: <20080503171627.GC23961@redhat.com> References: <20080503132327.GA28881@redhat.com> <481C77E8.8050002@redhat.com> <20080503171627.GC23961@redhat.com> Content-Type: text/plain Organization: Linux Solutions Group Date: Sat, 03 May 2008 16:05:07 -0600 Message-Id: <1209852307.5433.5.camel@hermosa.morrealenet> Mime-Version: 1.0 X-Mailer: Evolution 2.6.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2008-05-03 at 13:16 -0400, Frank Ch. Eigler wrote: > Hi - > > On Sat, May 03, 2008 at 09:34:16AM -0500, Clark Williams wrote: > > [...] > > > It has come to my attention that the preempt-rt patch suite > > > deliberately defeats the potential concurrency intended by systemtap's > > > use of rwlocks to permit concurrent readers [...] > > > The reason it "defeats" the concurrent behavior is that it's really > > complicated to have concurrent readers with Priority Inheritance, so > > the initial cut of rtmutexes serialized all lock accesses. [...] > > Do you believe priority inheritance to be an essential property of > every use of these primitives, regardless of the nature of the > specifical critical sections being protected? Is there no way & need > to opt out of the extra machinery? > > - FChE Yes, for (at least) two reasons. And No. Without PI the best case is indeterminate latencies. The worst case is deadlock. Please read Steven's excellent description of the issues in the Documentation directory of a kernel tree. Best, -PWM > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html