From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753649AbaGUVwc (ORCPT ); Mon, 21 Jul 2014 17:52:32 -0400 Received: from mail.skyhub.de ([78.46.96.112]:53737 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753019AbaGUVwa (ORCPT ); Mon, 21 Jul 2014 17:52:30 -0400 Date: Mon, 21 Jul 2014 23:52:25 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: Peter Zijlstra , Thomas Gleixner , x86-ml , lkml , Steven Rostedt Subject: Re: [PATCH] x86, TSC: Add a software TSC offset Message-ID: <20140721215225.GD11555@pd.tnic> References: <20140719130602.GA5101@pd.tnic> <53CD6B50.5010404@mit.edu> <20140721213534.GB11555@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 21, 2014 at 02:41:50PM -0700, Andy Lutomirski wrote: > How will this be compatible with the vdso? I've never thought about it yet. How compatible would you want it to be and what do you expect from it? Remember, this is only attempting to be a hardware workaround for a smallish number of systems out there. Most of current machines should have stable and synched TSCs. > Also, IIRC, rdtscp does not need rdtsc_barrier(), whereas rdtsc does. > Getting this wrong will be a significant slowdown. This is too cryptic for me - get_cycles doesn't barrier around the TSC now either. Again, we will most likely end up not using RDTSCP anyway. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --