From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752855AbbHUOen (ORCPT ); Fri, 21 Aug 2015 10:34:43 -0400 Received: from casper.infradead.org ([85.118.1.10]:38766 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751967AbbHUOem (ORCPT ); Fri, 21 Aug 2015 10:34:42 -0400 Date: Fri, 21 Aug 2015 16:34:15 +0200 From: Peter Zijlstra To: mingo@kernel.org, haiyangz@microsoft.com, tglx@linutronix.de, hpa@zytor.com, vkuznets@redhat.com, kys@microsoft.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/platform] x86/hyperv: Mark the Hyper-V TSC as unstable Message-ID: <20150821143415.GK3161@worktop.event.rightround.com> References: <1440003264-9949-1-git-send-email-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 21, 2015 at 12:45:50AM -0700, tip-bot for Vitaly Kuznetsov wrote: > Commit-ID: 88c9281a9fba67636ab26c1fd6afbc78a632374f > Gitweb: http://git.kernel.org/tip/88c9281a9fba67636ab26c1fd6afbc78a632374f > Author: Vitaly Kuznetsov > AuthorDate: Wed, 19 Aug 2015 09:54:24 -0700 > Committer: Ingo Molnar > CommitDate: Fri, 21 Aug 2015 08:44:38 +0200 > > x86/hyperv: Mark the Hyper-V TSC as unstable > > The Hyper-V top-level functional specification states, that > "algorithms should be resilient to sudden jumps forward or > backward in the TSC value", this means that we should consider > TSC as unstable. In some cases tsc tests are able to detect the > instability, it was detected in 543 out of 646 boots in my > testing: > > Measured 6277 cycles TSC warp between CPUs, turning off TSC clock. > tsc: Marking TSC unstable due to check_tsc_sync_source failed > > This is, however, just a heuristic. On Hyper-V platform there > are two good clocksources: MSR-based hyperv_clocksource and > recently introduced TSC page. *groan*.. and where are the paravirt ops like pv_time_ops for hyperv to fix up this mess?