From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753466Ab1LLSWN (ORCPT ); Mon, 12 Dec 2011 13:22:13 -0500 Received: from mx1.redhat.com ([209.132.183.28]:20675 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753398Ab1LLSWI (ORCPT ); Mon, 12 Dec 2011 13:22:08 -0500 Message-ID: <4EE6463A.2010007@redhat.com> Date: Mon, 12 Dec 2011 20:21:46 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 MIME-Version: 1.0 To: Alan Cox CC: Sasha Levin , Thomas Gleixner , Ingo Molnar , Pekka Enberg , LKML Subject: Re: [patch 0/3] kvm tool: Serial emulation overhaul References: <20111210132220.083204833@linutronix.de> <20111211103047.GA19299@elte.hu> <20111212102750.469f0d9f@pyramind.ukuu.org.uk> <1323687592.16450.0.camel@lappy> <20111212110236.755eda81@pyramind.ukuu.org.uk> In-Reply-To: <20111212110236.755eda81@pyramind.ukuu.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/12/2011 01:02 PM, Alan Cox wrote: > > > You can emulate a chip with a 64byte or so FIFO. You can do I/O cycle > > > prediction in the kernel part and you can use the empty bit as a clue > > > (which is what most serial<->ethernet widgetry does). > > > > The performance problems here aren't the same performance problems you > > have on real hardware. The problem here is that it costs 40k cycles for > > the guest to access the emulated chip. > > How much of that 40K cycles is bouncing back and forth into emulation > layers and how much of it is the kernel trap ? > 30K of those cycles are only in Sasha's mind, the real figure is 10K (and likely lower with newer hardware). -- error compiling committee.c: too many arguments to function