From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Alacrityvm-devel] [KVM PATCH v2 1/2] KVM: export lockless GSI attribute Date: Wed, 28 Oct 2009 12:04:00 +0200 Message-ID: <4AE81710.1080103@redhat.com> References: <20091023023512.3891.65889.stgit@dev.haskins.net> <20091023023845.3891.36857.stgit@dev.haskins.net> <4AE460F4.2090905@redhat.com> <4AE5A336.4010801@gmail.com> <4AE5C26A.9000400@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Gregory Haskins , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, alacrityvm-devel@lists.sourceforge.net To: Gregory Haskins Return-path: In-Reply-To: <4AE5C26A.9000400@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 10/26/2009 05:38 PM, Gregory Haskins wrote: >>> Instead of a lockless attribute, how about a ->set_atomic() method. For >>> msi this can be the same as ->set(), for non-msi it can be a function >>> that schedules the work (which will eventually call ->set()). >>> >>> The benefit is that we make a decision only once, when preparing the >>> routing entry, and install that decision in the routing entry instead of >>> making it again and again later. >>> >> Yeah, I like this idea. I think we can also get rid of the custom >> workqueue if we do this as well, TBD. >> > So I looked into this. It isn't straight forward because you need to > retain some kind of state across the deferment on a per-request basis > (not per-GSI). Today, this state is neatly tracked into the irqfd > object itself (e.g. it knows to toggle the GSI). > Yes, and it also contains the work_struct. What if we make the work_struct (and any additional state) part of the set_atomic() argument list? Does it simplify things? > So while generalizing this perhaps makes sense at some point, especially > if irqfd-like interfaces get added, it probably doesn't make a ton of > sense to expend energy on it ATM. It is basically a generalization of > the irqfd deferrment code. Lets just wait until we have a user beyond > irqfd for now. Sound acceptable? > I'll look at v3, but would really like to disentangle this. > In the meantime, I found a bug in the irq_routing code, so I will submit > a v3 with this fix, as well as a few other things I improved in the v2 > series. > > -- error compiling committee.c: too many arguments to function