On Mon, 4 Apr 2016 17:17:19 +0200 Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: > 2016-04-01 17:55-0400, Bandan Das: > > Hardik H Bagdi <hbagdi1@xxxxxxxxxxxxxx> writes: > >> Hello, > >> > >> For research, I am experimenting with increasing the number of > >> VCPUs in the guest OS. > >> I can increase the number of VCPUs till 255 in the guest OS but > >> more than that results in the following error- > > > > Radim (Cced) might have more info but the short answer is that you > > can't just simply increase the number. For >255, you need x2apic > > with interrupt remapping which is still missing. > > Yes, interrupt remapping is being developed for the split irqchip. > You could hack around that (we chose not to) so another blocker is > that QEMU cannot handle more than 255 VCPUs, mainly because of its AML > generator. Igor (Cc'd) knows more about the status of ACPI. I'm going to post patches that enable more than 255 VCPUs on ACPI side of QEMU once development window for 2.7 opens. > (And firmware doesn't implement x2APIC, and other minor problems ...) Firmware probably doesn't need more than 1 VCPU, maybe we can get rid of if it enumerating VCPUs via broadcast AP wakeup since it no longer builds ACPI tables anymore. It should save some boot time due to removing timeout for waiting APs wakeup. > All pieces should be in place within half a year, though. > The next hard limit is ~2^20 or ~2^32. In current version of my ACPI patches it's 2^32 limit so far. > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
