On May 4, 2008, at 9:56 AM, Avi Kivity wrote: > Marcelo Tosatti wrote: >> Add three PCI bridges to support 128 slots. >> >> Changes since v1: >> - Remove I/O address range "support" (so standard PCI I/O space is >> used). >> - Verify that there's no special quirks for 82801 PCI bridge. >> - Introduce separate flat IRQ mapping function for non-SPARC targets. >> >> > > I've cooled off on the 128 slot stuff, mainly because most real hosts > don't have them. An unusual configuration will likely lead to > problems > as most guest OSes and workloads will not have been tested thoroughly > with them.
This is more of a "let's do this conditionally" than a "let's not do it" reason imho. > - it requires a large number of interrupts, which are difficult to > provide, and which it is hard to ensure all OSes support. MSI is > relatively new. We could just as well extend the device layout to have every device be attached to one virtual IOAPIC pin, so we'd have like 128 / 4 = 32 IOAPICs in the system and one interrupt for each device. > - is only a few interrupts are available, then each interrupt requires > scanning a large number of queues This case should be rare, basically only existent with OSs that don't support APIC properly. > If we are to do this, then we need better tests than "80 disks show > up". True. > The alternative approach of having the virtio block device control > up to > 16 disks allows having those 80 disks with just 5 slots (and 5 > interrupts). This is similar to the way traditional SCSI controllers > behave, and so should not surprise the guest OS. The one thing I'm actually really missing here is use cases. What are we doing this for? And further along the line, are there other approaches to the problems for which this was supposed to be a solution? Maybe someone can raise a case where it's not virtblk / virtnet. Alex ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
