Re: [Qemu-devel] >256 Virtio-net-pci hotplug Devices

[Marcel Apfelbaum <marcel@redhat.com>]

On 24/07/2017 7:53, Kinsella, Ray wrote:
> 

Hi Ray,
Thank you for the details,

> 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.
> 

Even if I am not aware of how much time would take to init a bare-metal
PCIe Root Port, it seems too much.

> [   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.
> 

Assuming you are referring to legacy interrupts, maybe is possible
to disable them and use only MSI/MSI-X for PCIe Root Ports
(based on user input, we can't disable INTx for all the ports)


> [ 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.
> 

I would appreciate if you can share the results.

Thanks,
Marcel

> 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
>