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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 88F30C43464 for ; Fri, 18 Sep 2020 01:21:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48774208DB for ; Fri, 18 Sep 2020 01:21:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726185AbgIRBVF (ORCPT ); Thu, 17 Sep 2020 21:21:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:37998 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725886AbgIRBVE (ORCPT ); Thu, 17 Sep 2020 21:21:04 -0400 Received: from rorschach.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 89AFF2087D; Fri, 18 Sep 2020 01:21:03 +0000 (UTC) Date: Thu, 17 Sep 2020 21:21:01 -0400 From: Steven Rostedt To: Marco Elver Cc: Eric Dumazet , Peter Zijlstra , LKML , David Miller , Jakub Kicinski , netdev Subject: Re: [PATCH] random32: Use rcuidle variant for tracepoint Message-ID: <20200917212101.53287f29@rorschach.local.home> In-Reply-To: <20200821153532.GA3205540@elver.google.com> References: <20200821063043.1949509-1-elver@google.com> <20200821085907.GJ1362448@hirez.programming.kicks-ass.net> <20200821153532.GA3205540@elver.google.com> X-Mailer: Claws Mail 3.17.4git76 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Late reply, due to Plumbers followed by a much needed vacation and then drowning in 3 weeks of unread email! ] On Fri, 21 Aug 2020 17:35:32 +0200 Marco Elver wrote: > So, if the _rcuidle() variant here doesn't break your usecase, there > should be no harm in using the _rcuidle() variant. This also lifts the > restriction on where prandom_u32() is usable to what it was before, > which should be any context. > > Steven, Peter: What's the downside to of _rcuidle()? _rcuidle() only has a slightly more overhead in the tracing path (it's no different when not tracing). There's not a issue with _rcuidle() itself. The issue is that we need to have it. We'd like it to be that rcu *is* watching always except for a very minimal locations when switching context (kernel to and from user and running to and from idle), and then we just don't let tracing or anything that needs rcu in those locations. But for your patch: Acked-by: Steven Rostedt (VMware) -- Steve