From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH] uio: add irq control support to uio_pci_generic Date: Mon, 20 Apr 2015 08:33:18 -0700 Message-ID: <20150420083318.7b1e0cdb@urahara> References: <20150415095934.09966367@urahara> <20150416094105-mutt-send-email-mst@redhat.com> <20150416142110.2fc80b15@urahara> <20150420135906.GA26492@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "Hans J. Koch" , Greg Kroah-Hartman , kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20150420135906.GA26492@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, 20 Apr 2015 15:59:06 +0200 "Michael S. Tsirkin" wrote: > On Thu, Apr 16, 2015 at 02:21:10PM -0700, Stephen Hemminger wrote: > > On Thu, 16 Apr 2015 09:43:24 +0200 > > "Michael S. Tsirkin" wrote: > > > > > On Wed, Apr 15, 2015 at 09:59:34AM -0700, Stephen Hemminger wrote: > > > > The driver already supported INTX interrupts but had no in kernel > > > > function to enable and disable them. > > > > > > > > It is possible for userspace to do this by accessing PCI config > > > > directly, but this racy > > > > > > How is it racy? We have userspace using this interface, > > > if there's a race I want to fix it. > > > > There is nothing to prevent two threads in user space doing > > read/modify write at the same time. > > Well that's a userspace bug then - so let's drop that > from commit log lest people think this fixes some > kernel bugs. read/modify/write to the same register > is at least an easy to grasp problem, creating > an extra interface for the same function opens up > the possibility that some userspace will do > read/modify/write from one thread with irqcontrol > from another thread, creating more races. > > > The bigger issue is that DPDK needs to support multiple UIO > > interface types. And with current model there is no abstraction. > > The way to enable/disable IRQ is different depending on the UIO > > drivers. > > OK compatibility with other devices might be useful, but what are the > other UIO drivers DPDK supports? I only found support for igb_uio so > far, and that doesn't seem to be upstream. > Currently, supports: igb_uio, uio_pci_generic (as well as vfio) There are additional drivers which been submitted but not accepted for Xen and HyperV both of which require special uio drivers.