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vhost: Don't set vring call if guest notifier is unused

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The vring call fd is set even when the guest does not use MSI-X (e.g., in the
case of virtio PMD), leading to unnecessary CPU overhead for processing
interrupts.

The commit 96a3d98d2c("vhost: don't set vring call if no vector") optimized the
case where MSI-X is enabled but the queue vector is unset. However, there's an
additional case where the guest uses INTx and the INTx_DISABLED bit in the PCI
config is set, meaning that no interrupt notifier will actually be used.

In such cases, the vring call fd should also be cleared to avoid redundant
interrupt handling.

Fixes: 96a3d98d2c("vhost: don't set vring call if no vector")

Reported-by: Zhiyuan Yuan <yuanzhiyuan@chinatelecom.cn>
Signed-off-by: Jidong Xia <xiajd@chinatelecom.cn>
Signed-off-by: Huaitong Han <hanht2@chinatelecom.cn>
Message-Id: <20250522100548.212740-1-hanht2@chinatelecom.cn>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Huaitong Han 2025-05-22 18:05:48 +08:00 • committed by Michael S. Tsirkin
parent 82acc8c83f
commit a9403bfcd9
3 changed files with 8 additions and 2 deletions
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1
include/hw/pci/pci.h
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@ -983,6 +983,7 @@ void lsi53c8xx_handle_legacy_cmdline(DeviceState *lsi_dev);
qemu_irq pci_allocate_irq(PCIDevice *pci_dev);
void pci_set_irq(PCIDevice *pci_dev, int level);
int pci_irq_disabled(PCIDevice *d);
static inline void pci_irq_assert(PCIDevice *pci_dev)
{