From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751719Ab1LKKch (ORCPT ); Sun, 11 Dec 2011 05:32:37 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:59858 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751369Ab1LKKce (ORCPT ); Sun, 11 Dec 2011 05:32:34 -0500 Date: Sun, 11 Dec 2011 11:30:47 +0100 From: Ingo Molnar To: Pekka Enberg Cc: Thomas Gleixner , LKML , Sasha Levin Subject: Re: [patch 0/3] kvm tool: Serial emulation overhaul Message-ID: <20111211103047.GA19299@elte.hu> References: <20111210132220.083204833@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=AWL,BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] 0.0 AWL AWL: From: address is in the auto white-list Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Pekka Enberg wrote: > On Sat, 10 Dec 2011, Thomas Gleixner wrote: > > > There is a slight problem with them. I only tested them with > > the rt-guest kernels, but non rt kernels are slightly > > unhappy. Sorry for not thinking about that. > > > > Fix below. > > Applied, thanks! > > Ingo, how does serial console work for you with latest master? > It's likely that Thomas' patches fix top slowness for you. It didnt get worse - but i can still easily tell apart a 'top' running under kvm than native. Try something like this: run top and type 's0.1' to change the refresh interval to 100 msecs. Run the same thing under kvm and on the native host. The two are visibly different: the kvm one refreshes with the cursor showing up mid-refresh a number of times. In theory a kvm driven serial console should be extremely fast, much faster than a real serial console, basically as fast as a local console. Yet this still does not seem to be the case. In fact even ssh-ing in to a box over Wifi and running the above top session is undistinguishable from top running in a local console. So IMO it cannot be virtualization overhead - there must still be some delay or serious lack of buffering somewhere. Here's a way to measure the slowdown directly: time top -d 0.01 -n 10 -b native: 0.9 secs ssh over wifi: 1.4 secs kvm serial: 5.0 secs Thanks, Ingo