From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751146AbdE3Tke (ORCPT ); Tue, 30 May 2017 15:40:34 -0400 Received: from mga07.intel.com ([134.134.136.100]:19218 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751023AbdE3TkT (ORCPT ); Tue, 30 May 2017 15:40:19 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.38,419,1491289200"; d="scan'208";a="108365487" Date: Tue, 30 May 2017 12:40:17 -0700 From: Andi Kleen To: Peter Zijlstra Cc: Stephane Eranian , Vince Weaver , "Liang, Kan" , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "alexander.shishkin@linux.intel.com" , "acme@redhat.com" , "jolsa@redhat.com" , "torvalds@linux-foundation.org" , "tglx@linutronix.de" Subject: Re: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter Message-ID: <20170530194017.GN24144@tassilo.jf.intel.com> References: <20170524154518.GA24144@tassilo.jf.intel.com> <20170530092523.xkuj5lqpq5pb5y4m@hirez.programming.kicks-ass.net> <20170530135128.GI24144@tassilo.jf.intel.com> <20170530162838.h5tzdnrxpy6upbka@hirez.programming.kicks-ass.net> <20170530172208.GL24144@tassilo.jf.intel.com> <20170530174014.zjauj22hx7avxqgf@hirez.programming.kicks-ass.net> <20170530175151.GM24144@tassilo.jf.intel.com> <20170530185957.jxl5tfnqfyjot75x@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170530185957.jxl5tfnqfyjot75x@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > BTW there's an alternative solution in cycling the NMI watchdog over > > all available CPUs. Then it would eventually cover all. But that's > > less real time friendly than relying on RCU. > > I don't think we need to worry too much about the watchdog being rt > friendly. Robustness is the thing that worries me most. Ok. Then just cycling is the most robust method, and it's very simple. You're right. Perhaps it's better than to rely on the RCU machinery which seems to become ever more and more complex. People who care extremely about latencies can just turn it off. The main problem with the proposal is that it depends on the BIOS not locking the TCO watchdog. On the systems were it is locked we would either need to continue using the PMU for the watchdog, or find some other watchdog source that can be programmed to be a NMI. -Andi