On 01/03/12 00:34, Amos Kong wrote:
----- Original Message -----
On 2012-02-29 16:22, Amos Kong wrote:
----- Original Message -----
On 2012-02-29 14:30, Amos Kong wrote:
kvm_io_bus devices are used for ioevent, pit, pic, ioapic,
coalesced_mmio.
Currently Qemu only emulates one PCI bus, it contains 32 slots,
one slot contains 8 functions, maximum of supported PCI devices:
1 * 32 * 8 = 256. The maximum of coalesced mmio zone is 100,
each zone has an iobus devices. 300 io_bus devices is not enough.
This patch makes the kvm_io_range array can be resized
dynamically.
Is there any limit, or can userspace allocate arbitrary amounts of
kernel memory this way?
Hi Jan,
There is a fixed array in linux-2.6/include/linux/kvm_host.h,
we can only register 300 devices.
struct kvm_io_range {
gpa_t addr;
int len;
struct kvm_io_device *dev;
};
struct kvm_io_bus {
int dev_count;
#define NR_IOBUS_DEVS 300
struct kvm_io_range range[NR_IOBUS_DEVS];
};
^^^^^^^^^^^^^^
Right. But doesn't your patch remove precisely this limit? So what
limits userspace now? To register 300 million devices...?
Hi Jan,
It seems we need to reserve the limitation in kvm_host.h
#define NR_IOBUS_DEVS 600
/* Currently Qemu only emulates one PCI bus, it contains 32 slots,
one slot contains 8 functions. Only 29 slots can be used to
add multiple function devices. Maximum of supported PCI devices:
29 * 8 = 232. Each virtio-blk device needs 1 iobus device,
each virtio-net(vhost) device requires 2 such devices to service
notifications (ioevent) from rx/tx queues.
The maximum of coalesced mmio zone is 100, each zone has an iobus
devices. ioevent, pit, ioapic take less iobus devices.
So we can set max limitation to 600. */
One virtio-net(vhost=on) takes two iobus devices,
and it needs three IRQs for MSI/MIS-X.
I started a guest with 232 virtio-net(vhost=on),
guest IRQ 24 to 191 were used for virtio-config/input/output,
and only 56 virtio-nics' MSIX were enabled.
56 virtio-net(vhost=on) registered 56 * 2 = 112 iobus devices.
It's safe to set the limit to 300, right ?
----- check limit when register dev ----
virt/kvm/kvm_main.c:
/* Caller must hold slots_lock. */
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, struct kvm_io_device *dev)
{
struct kvm_io_bus *new_bus, *bus;
bus = kvm->buses[bus_idx];
if (bus->dev_count> NR_IOBUS_DEVS - 1) // can only register 600 devices
return -ENOSPC;
Amos.
--
Amos.
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