Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752468AbcD2HBc (ORCPT ); Fri, 29 Apr 2016 03:01:32 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:33226 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751910AbcD2HB3 (ORCPT ); Fri, 29 Apr 2016 03:01:29 -0400 MIME-Version: 1.0 In-Reply-To: <1461881913-23967-1-git-send-email-rjones@redhat.com> References: <1461881913-23967-1-git-send-email-rjones@redhat.com> From: "Matwey V. Kornilov" Date: Fri, 29 Apr 2016 10:01:08 +0300 X-Google-Sender-Auth: wlTKxWPKkxPOJsXcMjJbQZ4z0_s Message-ID: Subject: Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. To: "Richard W.M. Jones" Cc: Greg KH , Jiri Slaby , Peter Hurley , andriy.shevchenko@linux.intel.com, phillip.raffeck@fau.de, anton.wuerfel@fau.de, yamada.masahiro@socionext.com, valentinrothberg@gmail.com, linux-serial@vger.kernel.org, linux-kernel , ddutile@redhat.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1343 Lines: 34 2016-04-29 1:18 GMT+03:00 Richard W.M. Jones : > [This is an opinionated patch, mainly for discussion.] > > I'm trying to reduce the time taken in the kernel in initcalls, with > my aim being to reduce the current ~700ms spent in initcalls before > userspace, down to something like 100ms. All times on my Broadwell-U > laptop, under virtualization. The purpose of this is to be able to > launch VMs around containers with minimal overhead, like Intel Clear > Containers, but using standard distro kernels and qemu. > > Currently the kernel spends 25ms inspecting the UART that we passed to > it from qemu to find out whether it's an 8250/16550/16550A perhaps > with a non-working FIFO or other quirks. Well, it isn't -- it's a > working emulated 16550A, with a FIFO and no quirks, and if it isn't, > we should fix qemu. > > So the patch detects if we're running virtualized (perhaps it should > only check for qemu/KVM?) and if so, shortcuts the tests. Does anybody know, whether it is possible to pass through real hardware serial port to a guest? It seems to be as simple as to pass through an interrupt and memory IO ports. > > Rich. > -- With best regards, Matwey V. Kornilov. Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia 119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382