From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01717C46470 for ; Wed, 8 Aug 2018 15:27:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1A0521A14 for ; Wed, 8 Aug 2018 15:27:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1A0521A14 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727489AbeHHRrS (ORCPT ); Wed, 8 Aug 2018 13:47:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:55854 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727069AbeHHRrS (ORCPT ); Wed, 8 Aug 2018 13:47:18 -0400 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 545E721990; Wed, 8 Aug 2018 15:27:07 +0000 (UTC) Date: Wed, 8 Aug 2018 11:27:05 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: Joel Fernandes , Joel Fernandes , LKML , "Cc: Android Kernel" , Boqun Feng , Byungchul Park , Ingo Molnar , Masami Hiramatsu , Mathieu Desnoyers , Namhyung Kim , Peter Zijlstra , Thomas Glexiner , Tom Zanussi Subject: Re: [PATCH v12 3/3] tracing: Centralize preemptirq tracepoints and unify their usage Message-ID: <20180808112705.22e6a96d@gandalf.local.home> In-Reply-To: <20180808144200.GM24813@linux.vnet.ibm.com> References: <6D0A3FD6-2190-4CC0-A3C0-7B3759E73243@google.com> <20180807204820.50b83c6d@vmware.local.home> <20180807215522.04114097@vmware.local.home> <20180807222856.3ede96e7@vmware.local.home> <20180808130041.GI24813@linux.vnet.ibm.com> <20180808102700.38c4169d@gandalf.local.home> <20180808144200.GM24813@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 8 Aug 2018 07:42:00 -0700 "Paul E. McKenney" wrote: > > There's also a local_inc() if you are using per cpu pointers, that is > > suppose to guarantee atomicity for single cpu operations. That's what > > the ftrace ring buffer uses. > > Good point, that becomes atomic_long_inc() or equivalent on most > architectures, but an incl instruction (not locked) on x86. So updating > my earlier still-untested thought: > > int __srcu_read_lock_nmi(struct srcu_struct *sp) /* UNTESTED. */ > { > int idx; > > idx = READ_ONCE(sp->srcu_idx) & 0x1; > local_inc(&sp->sda->srcu_lock_count[idx]); > smp_mb__after_atomic(); /* B */ /* Avoid leaking critical section. */ > return idx; > } > > void __srcu_read_unlock_nmi(struct srcu_struct *sp, int idx) > { > smp_mb__before_atomic(); /* C */ /* Avoid leaking critical section. */ > local_inc(&sp->sda->srcu_unlock_count[idx]); > } > > Would that work, or is there a better way to handle this? This would work much better than using the atomic ops, and I think it would be doable. I may need to revert the srcu for trace_*_rcidle() for now, as I want most of the other changes in this merge window, and it's getting too late to do it with these updates. -- Steve