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* vfio_pin_map_dma cause synchronize_sched wait too long
@ 2019-12-02  9:10 Longpeng (Mike)
  2019-12-02  9:31 ` Paolo Bonzini
  0 siblings, 1 reply; 5+ messages in thread
From: Longpeng (Mike) @ 2019-12-02  9:10 UTC (permalink / raw)
  To: Alex Williamson, pbonzini
  Cc: qemu-devel, kvm, linux-kernel, Longpeng(Mike), Gonglei, Huangzhichao

Hi guys,

Suppose there're two VMs: VM1 is bind to node-0 and calling vfio_pin_map_dma(),
VM2 is a migrate incoming VM which bind to node-1. We found the vm_start( QEMU
function) of VM2 will take too long occasionally, the reason is as follow.

- VM2 -
qemu: vm_start
        vm_start_notify
          virtio_vmstate_change
            virtio_pci_vmstate_change
              virtio_pci_start_ioeventfd
                virtio_device_start_ioeventfd_impl
                  event_notifier_init
                    eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC) <-- too long
kern: sys_eventfd2
        get_unused_fd_flags
          __alloc_fd
            expand_files
              expand_fdtable
                synchronize_sched <-- too long

- VM1 -
The VM1 is doing vfio_pin_map_dma at the same time.

The CPU must finish vfio_pin_map_dma and then rcu-sched grace period can be
elapsed, so synchronize_sched would wait for a long time.

Is there any solution to this ? Any suggestion would be greatly appreciated, thanks!

-- 
Regards,
Longpeng(Mike)


^ permalink raw reply	[flat|nested] 5+ messages in thread

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Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-12-02  9:10 vfio_pin_map_dma cause synchronize_sched wait too long Longpeng (Mike)
2019-12-02  9:31 ` Paolo Bonzini
2019-12-02  9:42   ` Longpeng (Mike)
2019-12-02 10:06     ` Paolo Bonzini
2019-12-02 10:47       ` Longpeng (Mike)

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