From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756217Ab3JGRkx (ORCPT ); Mon, 7 Oct 2013 13:40:53 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42505 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753218Ab3JGRkv (ORCPT ); Mon, 7 Oct 2013 13:40:51 -0400 Date: Mon, 7 Oct 2013 19:40:37 +0200 From: Peter Zijlstra To: "H. Peter Anvin" Cc: Ingo Molnar , Adrian Hunter , linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/core] perf/x86: Clean up cap_user_time* setting Message-ID: <20131007174037.GI3081@twins.programming.kicks-ass.net> References: <524F097A.9010506@intel.com> <20131004185539.GT15690@laptop.programming.kicks-ass.net> <20131006091054.GA4342@gmail.com> <5252EDBE.7030805@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5252EDBE.7030805@zytor.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 07, 2013 at 10:22:06AM -0700, H. Peter Anvin wrote: > CONFIG_X86_TSC is a baseline control option; we shouldn't key > functionality off of it. It's fine to say notsc -> no tracing, but > making it a compile-time key makes me a bit uphappy. We cut off 386, > but cutting of 486 at this point makes me nervous. The thing that annoys me about notsc is that it disables usage even if its present. I've no problem with 486 which simply doesn't have TSC and thus cpu_has_tsc will be false and other stuff will happen -- and I don't think my proposition would actually change anything there. What is completely insane is people using notsc on say a haswell chip and expecting something sane to happen. So I'm not proposing we remove !cap_has_tsc support; all I'm proposing is we remove the notsc knob that avoids using the TSC on perfectly good hardware.