From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Host latency peaks due to kvm-intel Date: Thu, 23 Jul 2009 20:07:33 +0200 Message-ID: <4A68A6E5.6010808@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: RT To: kvm-devel Return-path: Received: from lizzard.sbs.de ([194.138.37.39]:16587 "EHLO lizzard.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751908AbZGWSHk (ORCPT ); Thu, 23 Jul 2009 14:07:40 -0400 Sender: kvm-owner@vger.kernel.org List-ID: Hi, did anyone recently tried current KVM for Intel over some real-time Linux? I'm seeing more than 500 us latency peaks on the host, specifically during VM startup. This applies to both 2.6.29.6-rt23 and Xenomai/I-pipe. For -rt, I both tried the included (patched) KVM modules as well as kvm.git head with some additionally required -rt fixes. Xenomai ran over a 2.6.30 kernel with my own KVM-enabler patch. Early instrumentation actually points to the guest exit itself: I added markers right before and after the assembly part of vmx_vcpu_run, and further instrumentation reports that the next host APIC tick should go off right inside guest mode. But KVM leaves the switching part 500 us too late in that case - as if guest exit on external IRQs was disabled. Will debug this further, but I'm also curious to hear other user experiences. Jan -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux