With regard to old version linux guest(e.g., rhel-5.5), in ISR processing, mask
and unmask msi-x vector every time, which result in VMEXIT, then QEMU will
invoke kvm_irqchip_update_msi_route() to ask KVM hypervisor to update the VM
irq routing table. In KVM hypervisor, synchronizing RCU needed after updating
routing table, so much time consumed for waiting in wait_rcu_gp(). So CPU usage
in VM is so high, while from the view of host, VM's total CPU usage is so low.
Masking/unmasking msi-x vector only set msi-x entry "control" section, needless
to update VM irq routing table.
Signed-off-by: Zhang Haoyu <haoyu.zh...@huawei.com>
Signed-off-by: Huang Weidong <weidong.hu...@huawei.com>
Signed-off-by: Qin Chuanyu <qinchua...@huawei.com>
---
hw/i386/kvm/pci-assign.c | 3 +++
1 files changed, 3 insertions(+)
--- a/hw/i386/kvm/pci-assign.c 2013-05-04 15:53:18.000000000 +0800
+++ b/hw/i386/kvm/pci-assign.c 2013-05-04 15:50:46.000000000 +0800
@@ -1576,6 +1576,8 @@ static void assigned_dev_msix_mmio_write
MSIMessage msg;
int ret;
+ /* Needless to update msi route when only msi-x entry
"control" section changed */
+ if ((addr & (PCI_MSIX_ENTRY_SIZE - 1)) !=
PCI_MSIX_ENTRY_VECTOR_CTRL){
msg.address = entry->addr_lo |
((uint64_t)entry->addr_hi << 32);
msg.data = entry->data;
@@ -1585,6 +1587,7 @@ static void assigned_dev_msix_mmio_write
if (ret) {
error_report("Error updating irq routing entry (%d)", ret);
}
+ }
}
}
}
Thanks,
Zhang Haoyu
