Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758551AbYH2Q6W (ORCPT ); Fri, 29 Aug 2008 12:58:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754922AbYH2Q6K (ORCPT ); Fri, 29 Aug 2008 12:58:10 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:43270 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754920AbYH2Q6I (ORCPT ); Fri, 29 Aug 2008 12:58:08 -0400 Date: Fri, 29 Aug 2008 12:58:05 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Gregory Haskins cc: Andi Kleen , Gregory Haskins , mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org Subject: Re: [PATCH] seqlock: serialize against writers In-Reply-To: <48B8254D.1010206@gmail.com> Message-ID: References: <20080829154237.1196.66825.stgit@dev.haskins.net> <87abevpzv7.fsf@basil.nowhere.org> <48B81F60.3080409@gmail.com> <20080829162216.GW26610@one.firstfloor.org> <48B82349.1020109@gmail.com> <48B8254D.1010206@gmail.com> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1344 Lines: 33 On Fri, 29 Aug 2008, Gregory Haskins wrote: > > Yeah, ideas crossed in the mail ;) > > I could just force all of the seqbegins to hit the slowpath by hacking > the code and see what happens (aside from slowing down, of course ;) > > Question: Which seqlock_t does userspace use? I assume it uses > seqlock_t and not raw_seqlock_t. But the only reason that I ask is that > I converted raw_seqlock_t to use the new style as well to be consistent, > even though it is not strictly necessary for the same reasons. So if > perchance userspace uses the raw variant, I could solve this issue by > only re-working the seqlock_t variant. Kind of a long shot, but figured > I would mention it :) I answered this on IRC, but this is for the rest of those reading this thread. Userspace (vsyscalls) can only use raw_seqlock_t. And only the read version for that matter. Since the read of raw_seqlock_t is just that, a read, no writes, and no jumping to other functions on contention. The vsyscalls should never use the -rt seqlock_t. Not modifying the raws here should make us golden. -- 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/