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[PATCH] hw/virtio: Add ioeventfd option for balloon


From: Zheyun Shen
Subject: [PATCH] hw/virtio: Add ioeventfd option for balloon
Date: Tue, 12 Dec 2023 15:50:58 +0800

Traditional mmio in balloon makes qemu do balloon inflation in the same
thread as vcpu thread.In a CPU overcommitment scenario, host may run
more than one vcpu threads on one host thread, which makes
madvise_dontneed_free() wait for a long time due to the function
cond_resched() at host side.

If using SEV/ES and the kernel provided by AMD, the overhead will
become even much larger.

With ioeventfd, the thread for host to do balloon inflation will
be seperated from the vcpu thread, leading to better performance
for the whole process of balloon inflation.

Signed-off-by: Zheyun Shen <szy0127@sjtu.edu.cn>
---
 hw/virtio/virtio-balloon-pci.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/virtio/virtio-balloon-pci.c b/hw/virtio/virtio-balloon-pci.c
index ce2645b..7195322 100644
--- a/hw/virtio/virtio-balloon-pci.c
+++ b/hw/virtio/virtio-balloon-pci.c
@@ -35,6 +35,12 @@ struct VirtIOBalloonPCI {
     VirtIOBalloon vdev;
 };
 
+static Property virtio_balloon_properties[] = {
+    DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
+            VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void virtio_balloon_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
 {
     VirtIOBalloonPCI *dev = VIRTIO_BALLOON_PCI(vpci_dev);
@@ -51,6 +57,7 @@ static void virtio_balloon_pci_class_init(ObjectClass *klass, 
void *data)
     PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
     k->realize = virtio_balloon_pci_realize;
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+    device_class_set_props(dc, virtio_balloon_properties);
     pcidev_k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
     pcidev_k->device_id = PCI_DEVICE_ID_VIRTIO_BALLOON;
     pcidev_k->revision = VIRTIO_PCI_ABI_VERSION;
-- 
2.34.1




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