From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752169AbeCTJJj (ORCPT ); Tue, 20 Mar 2018 05:09:39 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:55064 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751533AbeCTJJi (ORCPT ); Tue, 20 Mar 2018 05:09:38 -0400 Date: Tue, 20 Mar 2018 10:09:31 +0100 From: Peter Zijlstra To: "Liu, Changcheng" Cc: tglx@linutronix.de, hpa@zytor.com, douly.fnst@cn.fujitsu.com, linux-kernel@vger.kernel.org, "Stanton, Kevin B" Subject: Re: [PATCH] x86/ioapic: don't use unstable TSC to detect timer IRQ Message-ID: <20180320090931.GQ4043@hirez.programming.kicks-ass.net> References: <20180320084255.GA187704@sofia> <20180320084929.GP4043@hirez.programming.kicks-ass.net> <20180320085835.GA56497@sofia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180320085835.GA56497@sofia> User-Agent: Mutt/1.9.3 (2018-01-21) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 20, 2018 at 04:58:35PM +0800, Liu, Changcheng wrote: > On 09:49 Tue 20 Mar, Peter Zijlstra wrote: > > On Tue, Mar 20, 2018 at 04:42:55PM +0800, Liu, Changcheng wrote: > > > In rare case, the TSC is every unstable or can't sync with > > > real time hardware clock. > > > > However did you manage that? Please provide _FAR_ more details. > [Changcheng] TSC is simulated and HPET is hardware implemented. > TSC can't sync with HPET. When running linux, the TSC grows too > fast and HPET can't trigger periodic timer interrupt in time which > is used to update jiffies. How is that not utterly broken, and how is that even allowed behaviour as per the SDM ? If the TSC is so utterly broken as to not function according to spec, you should not advertise the TSC, at which point you'll find that it is _very_ hard to run modern linux on x86 without TSC.