From: Avi Kivity Subject: Re: [PATCH 0/2] eventfd: new EFD_STATE flag Date: Thu, 20 Aug 2009 20:38:48 +0300 Message-ID: <4A8D8A28.2050004@redhat.com> References: <20090820155655.GA8764@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , gleb@redhat.com, kvm@vger.kernel.org, Linux Kernel Mailing List To: Davide Libenzi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:4122 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754965AbZHTRiR (ORCPT ); Thu, 20 Aug 2009 13:38:17 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 08/20/2009 07:20 PM, Davide Libenzi wrote: > > I briefly looked at this while in vacation, although I did not reply > hoping the horrible feeling about this code would go away. > It didn't. > I find this to be an ugly and ad-hoc multiplexing of eventfd with added > functionalities of questionable general use. > I'm pretty sure you can do better on KVM side, to solve the problem w/out > littering eventfd. > > While we could argue about this my feeling is that we should drop this, at least until we can quantify what benefit it has and whether there are any Davide-acceptable alternatives. In the meanwhile, we can let vhost-net support edge-triggered interrupts only, let qemu terminate those eventfds and convert then to level-triggered interrupts (which it can then inject using the existing ioctl). It will keep vhost-net and kvm simpler at the cost of some performance penalty to guests using level interrupts. These suck anyway so we'll point users at msi. -- I have a truly marvellous patch that fixes the bug which thisb signature is too narrow to contain.