From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: [patch 0/7] force the TSC unreliable by reporting C2 state Date: Wed, 18 Jun 2008 13:42:05 -0300 Message-ID: <20080618164205.108219607@localhost.localdomain> Cc: kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([66.187.233.31]:60220 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752681AbYFRQw2 (ORCPT ); Wed, 18 Jun 2008 12:52:28 -0400 Sender: kvm-owner@vger.kernel.org List-ID: Avi, I don't think this causes such a huge performance regression. NOHZ makes the frequency of timer reads go down significantly. As for constant tick guests, well, the impact will be similar to changing to SMP, since those fallback to ACPI timer anyway now. The C2 emulation is required by Ubuntu 7.10 for example, which refuses to process the CST notification. Stock Linux kernels (as old as 2.6.20) do mark C2 invalid upon the CST notification. --