So as it turns out at 512 devices, it is nothing to do SeaBIOS, it was the Kernel again. It is taking quite a while to startup, a little over two hours (7489 seconds). The main culprits appear to be enumerating/initializing the PCI Express ports and enabling interrupts.
The PCI Express Root Ports are taking a long time to enumerate/ initializing. 42 minutes in total=2579/60=64 ports in total, 40 seconds each.
[ 50.612822] pci_bus 0000:80: root bus resource [bus 80-c1] [ 172.345361] pci 0000:80:00.0: PCI bridge to [bus 81] ... [ 2724.734240] pci 0000:80:08.0: PCI bridge to [bus c1] [ 2751.154702] ACPI: Enabled 2 GPEs in block 00 to 3F
I assume the 1 hour (3827 seconds) below is being spent enabling interrupts.
[ 2899.394288] ACPI: PCI Interrupt Link [GSIG] enabled at IRQ 22 [ 2899.531324] ACPI: PCI Interrupt Link [GSIH] enabled at IRQ 23 [ 2899.534778] ACPI: PCI Interrupt Link [GSIE] enabled at IRQ 20 [ 6726.914388] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled [ 6726.937932] 00:04: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A [ 6726.964699] Linux agpgart interface v0.103
There finally there is another 20 minutes to find in the boot.
[ 7489.202589] virtio_net virtio515 enp193s0f0: renamed from eth513
Poky (Yocto Project Reference Distro) 2.3 qemux86-64 ttyS0
qemux86-64 login: root
I will remove the virtio-net-pci devices and hotplug them instead. In theory it should improve boot time, at expense of incurring some of these costs at runtime.
Ray K
-----Original Message----- From: Kevin O'Connor [mailto:kevin@koconnor.net] Sent: Sunday, July 23, 2017 1:05 PM To: Marcel Apfelbaum marcel@redhat.com; Kinsella, Ray ray.kinsella@intel.com Cc: qemu-devel@nongnu.org; seabios@seabios.org; Gerd Hoffmann kraxel@redhat.com; Michael Tsirkin mst@redhat.com Subject: Re: >256 Virtio-net-pci hotplug Devices
On Sun, Jul 23, 2017 at 07:28:01PM +0300, Marcel Apfelbaum wrote:
On 22/07/2017 2:57, Kinsella, Ray wrote:
When scaling up to 512 Virtio-net devices SeaBIOS appears to really slow down when configuring PCI Config space - haven't manage to get this to work yet.
If there is a slowdown in SeaBIOS, it would help to produce a log with timing information - see: https://www.seabios.org/Debugging#Timing_debug_messages
It may also help to increase the debug level in SeaBIOS to get more fine grained timing reports.
-Kevin