From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [PATCH 0/6] IRQFD without IRQ routing, enabled for XICS Date: Mon, 30 Jun 2014 14:43:56 +0200 Message-ID: <53B15B8C.5020909@suse.de> References: <1404125474-18611-1-git-send-email-paulus@samba.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , Eric Auger To: Paul Mackerras , kvm@vger.kernel.org, kvm-ppc@vger.kernel.org Return-path: Received: from cantor2.suse.de ([195.135.220.15]:43087 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752218AbaF3Mn7 (ORCPT ); Mon, 30 Jun 2014 08:43:59 -0400 In-Reply-To: <1404125474-18611-1-git-send-email-paulus@samba.org> Sender: kvm-owner@vger.kernel.org List-ID: On 30.06.14 12:51, Paul Mackerras wrote: > This series of patches provides a way to implement IRQFD support > without having to implement IRQ routing, and adds IRQFD support for > the XICS interrupt controller emulation. (XICS is the interrupt > controller defined for the pSeries machine type, used on IBM POWER > servers). > > The basic approach is to make it easy for code other than irqchip.c to > provide a mapping from a global interrupt number (GSI) to an irq > routing entry (struct kvm_kernel_irq_routing_entry). To make the > lifetime of this routing entry easier to manage, we change the IRQFD > code to keep a copy of the routing entry (for the MSI fast-path case) > rather than a pointer to the routing entry. Since the copy can't be > updated atomically, we add a seqcount_t to make sure that when reading > it we get a copy that hasn't been half-way updated. > > Next we replace the hard-coded accesses outside irqchip.c to the > fields of the kvm_irq_routing_table struct with calls to accessor > functions in irqchip.c, namely kvm_irq_map_gsi() and > kvm_irq_map_chip_pin(). That enables us to move all references to the > kvm_irq_routing_table struct, and the definition of that struct, into > irqchip.c. > > Then we move the irq notifier implementation from irqchip.c into > eventfd.c and add a separate Kconfig option to enable IRQFD. With > that we can enable IRQFD without irq routing, which we achieve by > compiling in eventfd.c but not irqchip.c, and providing an alternative > implementation of kvm_irq_map_gsi() and kvm_irq_map_chip_pin(). > > The last patch does that for XICS. With this series I can use > vhost-net with KVM guests, and I see the TCP bandwidth between guest > and host on a POWER8 machine go from around 700MB/s to over 2GB/s. > > I would like to see this go into 3.17. I think this approach is good enough for XICS, as it has a 100% flat number space. I'm not yet fully convinced how well this would work out with the GIC, but I know that one too little to make claims. The only thing I disliked about this patch set is that it adds another piece of code that makes MPIC/XICS exclusive options. But I don't think that'd be hard to solve if we start caring. Overall, nice work. Alex