From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH v4 0/9] KVM: Improve IRQ assignment for device passthrough Date: Tue, 16 Nov 2010 14:55:07 -0200 Message-ID: <20101116165506.GA20186@amt.cnet> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , kvm , Alex Williamson , "Michael S. Tsirkin" To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:17938 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756446Ab0KPSLU (ORCPT ); Tue, 16 Nov 2010 13:11:20 -0500 Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Nov 08, 2010 at 12:21:44PM +0100, Jan Kiszka wrote: > Nine patches (yeah, it's getting more and more) to improve "classic" > device assigment /wrt IRQs. Highlight is the last one that resolves the > host IRQ sharing issue for all PCI 2.3 devices. Quite essential when > passing non-MSI-ready devices like many USB host controllers. > > As there were concerns regarding the overhead of IRQ masking via the PCI > config space, I did some micro-benchmarks. Well, the concerns are valid: > > disable_irq_nosync: ~600 cycles > pci_2_3_irq_check_and_mask: ~6000 cycles (EHCI) > ~22000 cycles (AR9287, with peaks >100000) > > Specifically the varying impact of the device like in the Atheros case > is worrying (this device is actually known to cause horrible latencies > to the host, but who knows what other devices do). So I decided to go > with PCI-2.3 masking as default off in the to-be-sent qemu-kvm patch. > Maybe something to consider vor VFIO as well. Looks fine to me. Michael, Alex? Also needs a rebase.