Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932425AbdGKJCz (ORCPT ); Tue, 11 Jul 2017 05:02:55 -0400 Received: from merlin.infradead.org ([205.233.59.134]:50090 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755242AbdGKJCy (ORCPT ); Tue, 11 Jul 2017 05:02:54 -0400 Date: Tue, 11 Jul 2017 11:02:40 +0200 From: Peter Zijlstra To: Andi Kleen Cc: Aubrey Li , tglx@linutronix.de, len.brown@intel.com, rjw@rjwysocki.net, tim.c.chen@linux.intel.com, arjan@linux.intel.com, paulmck@linux.vnet.ibm.com, yang.zhang.wz@gmail.com, x86@kernel.org, linux-kernel@vger.kernel.org, Aubrey Li Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods Message-ID: <20170711090240.az5rabtlzpupbrq5@hirez.programming.kicks-ass.net> References: <1499650721-5928-1-git-send-email-aubrey.li@intel.com> <20170710084647.zs6wkl3fumszd33g@hirez.programming.kicks-ass.net> <20170710144609.GD31832@tassilo.jf.intel.com> <20170710164206.5aon5kelbisxqyxq@hirez.programming.kicks-ass.net> <20170710172705.GA3441@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170710172705.GA3441@tassilo.jf.intel.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 599 Lines: 15 On Mon, Jul 10, 2017 at 10:27:05AM -0700, Andi Kleen wrote: > On Mon, Jul 10, 2017 at 06:42:06PM +0200, Peter Zijlstra wrote: > > I have, and last time I did the actual poking at the LAPIC (to make NOHZ > > happen) was by far the slowest thing happening. > > That must have been a long time ago because modern systems use TSC deadline > for a very long time ... Its been a while, but I didn't use the very latest chip when I did. > It's still slow, but not as slow as the LAPIC. Deadline TSC is a LAPIC timer mode. Sure the MSR might be slightly cheaper than the MMIO, but its still painful.