From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:48127) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RgIf5-0001ci-G7 for qemu-devel@nongnu.org; Thu, 29 Dec 2011 11:17:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RgIf4-0007B5-IX for qemu-devel@nongnu.org; Thu, 29 Dec 2011 11:16:59 -0500 Received: from mail-yw0-f45.google.com ([209.85.213.45]:51627) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RgIf4-0007Aw-Fh for qemu-devel@nongnu.org; Thu, 29 Dec 2011 11:16:58 -0500 Received: by yhgg71 with SMTP id g71so9659713yhg.4 for ; Thu, 29 Dec 2011 08:16:58 -0800 (PST) Message-ID: <4EFC9277.9040604@codemonkey.ws> Date: Thu, 29 Dec 2011 10:16:55 -0600 From: Anthony Liguori MIME-Version: 1.0 References: <20111219083141.32311.9429.stgit@abhimanyu.in.ibm.com> <20111219112326.GA15090@elte.hu> <87sjke1a53.fsf@abhimanyu.in.ibm.com> <4EF1B85F.7060105@redhat.com> <877h1o9dp7.fsf@linux.vnet.ibm.com> <20111223103620.GD4749@elte.hu> <4EF701C7.9080907@redhat.com> <87vcp4t45p.fsf@linux.vnet.ibm.com> <4EF838BD.60406@redhat.com> <4EFC903C.3030509@redhat.com> In-Reply-To: <4EFC903C.3030509@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Better qemu/kvm defaults (was Re: [RFC PATCH 0/4] Gang scheduling in CFS) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: dlaor@redhat.com Cc: kvm-devel , Anthony Liguori , Avi Kivity , Nikunj A Dadhania , qemu-devel On 12/29/2011 10:07 AM, Dor Laor wrote: > On 12/26/2011 11:05 AM, Avi Kivity wrote: >> On 12/26/2011 05:14 AM, Nikunj A Dadhania wrote: >>>> >>>> btw you can get an additional speedup by enabling x2apic, for >>>> default_send_IPI_mask_logical(). >>>> >>> In the host? >>> >> >> In the host, for the guest: >> >> qemu -cpu ...,+x2apic >> > > It seems to me that we should improve our default flags. > So many times users fail to submit the proper huge command-line options that we > require. Honestly, we can't blame them, there are so many flags and so many use > cases its just too hard to get it right for humans. > > I propose a basic idea and folks are welcome to discuss it: > > 1. Improve qemu/kvm defaults > Break the current backward compatibility (but add a --default- > backward-compat-mode) and set better values for: > - rtc slew time What do you specifically mean? > - cache=none I'm not sure I see this as a "better default" particularly since O_DIRECT fails on certain file systems. I think we really need to let WCE be toggable from the guest and then have a caching mode independent of WCE. We then need some heuristics to only enable cache=off when we know it's safe. > - x2apic, maybe enhance qemu64 or move to -cpu host? Alex posted a patch for this. I'm planning on merging it although so far no one has chimed up either way. > - aio=native|threads (auto-sense?) aio=native is unsafe to default because linux-aio is just fubar. It falls back to synchronous I/O if the underlying filesystem doesn't support aio. There's no way in userspace to problem if it's actually supported or not either... > - use virtio devices by default I don't think this is realistic since appropriately licensed signed virtio drivers do not exist for Windows. (Please note the phrase "appropriately licensed signed"). > - more? > > Different defaults may be picked automatically when TCG|KVM used. > > 2. External hardening configuration file kept in qemu.git > For non qemu/kvm specific definitions like the io scheduler we > should maintain a script in our tree that sets/sense the optimal > settings of the host kernel (maybe similar one for the guest). What are "appropriate host settings" and why aren't we suggesting that distros and/or upstream just set them by default? Regards, Anthony Liguori > HTH, > Dor >