Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765973AbXHXS5O (ORCPT ); Fri, 24 Aug 2007 14:57:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760996AbXHXS47 (ORCPT ); Fri, 24 Aug 2007 14:56:59 -0400 Received: from ms-smtp-03.nyroc.rr.com ([24.24.2.57]:35076 "EHLO ms-smtp-03.nyroc.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759759AbXHXS46 (ORCPT ); Fri, 24 Aug 2007 14:56:58 -0400 Date: Fri, 24 Aug 2007 14:56:13 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: john stultz cc: Ingo Molnar , LKML , RT , Thomas Gleixner Subject: Re: [PATCH RT 3/3] fix get_monotonic_cycles for latency tracer In-Reply-To: <1187980244.6163.13.camel@localhost.localdomain> Message-ID: References: <1187978236.2941.19.camel@localhost.localdomain> <1187980244.6163.13.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1004 Lines: 35 -- On Fri, 24 Aug 2007, john stultz wrote: > > > > - /* calculate the delta since the last update_wall_time: */ > > - cycle_delta = (cycle_now - clock->cycle_last) & clock->mask; > > + } while (cycle_raw != clock->cycle_raw || > > + cycle_last != clock->cycle_last); > > So if I'm understanding this right, not taking a lock isn't an > optimization (as the seq read lock code is almost the same), but a > requirement (as this might be called while xtime_lock is held), > correct? Exactly. The latency tracer uses this so no locks can be grabbed (seq_locks included). > > Might want to clarify that a bit in the comment. > OK, will do and send a updated patch. I wasn't in the best state writing this patch in the wee hours of the night ;-) -- Steve - 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/