This change, combined with the compiler hint to inline get_used_event,
shortens the window between the memory read and the actual check by
calling get_used_event from needs_notification.
Without it, when putting enough pressure on the vring, it's possible
that a notification is wrongly omitted, causing the queue to stall.
Signed-off-by: Sergio Lopez <slp@redhat.com>
Now that vhost_user_backend and vm-virtio do support EVENT_IDX, use it
in vhost_user_block to reduce the number of notifications sent between
the driver and the device.
This is specially useful when using active polling on the virtqueue,
as it'll be implemented by a future patch.
This is a snapshot of kvm_stat while generating ~60K IOPS with fio on
the guest without EVENT_IDX:
Event Total %Total CurAvg/s
kvm_entry 393454 20.3 62494
kvm_exit 393446 20.3 62494
kvm_apic_accept_irq 378146 19.5 60268
kvm_msi_set_irq 369720 19.0 58881
kvm_fast_mmio 370497 19.1 58817
kvm_hv_timer_state 10197 0.5 1715
kvm_msr 8770 0.5 1443
kvm_wait_lapic_expire 7018 0.4 1118
kvm_apic 2768 0.1 538
kvm_pv_tlb_flush 2028 0.1 360
kvm_vcpu_wakeup 1453 0.1 278
kvm_apic_ipi 1384 0.1 269
kvm_fpu 1148 0.1 164
kvm_pio 574 0.0 82
kvm_userspace_exit 574 0.0 82
kvm_halt_poll_ns 24 0.0 3
And this is the snapshot while doing the same thing with EVENT_IDX:
Event Total %Total CurAvg/s
kvm_entry 35506 26.0 3873
kvm_exit 35499 26.0 3873
kvm_hv_timer_state 14740 10.8 1672
kvm_apic_accept_irq 13017 9.5 1438
kvm_msr 12845 9.4 1421
kvm_wait_lapic_expire 10422 7.6 1118
kvm_apic 3788 2.8 502
kvm_pv_tlb_flush 2708 2.0 340
kvm_vcpu_wakeup 1992 1.5 258
kvm_apic_ipi 1894 1.4 251
kvm_fpu 1476 1.1 164
kvm_pio 738 0.5 82
kvm_userspace_exit 738 0.5 82
kvm_msi_set_irq 701 0.5 69
kvm_fast_mmio 238 0.2 4
kvm_halt_poll_ns 50 0.0 1
kvm_ple_window_update 28 0.0 0
kvm_page_fault 4 0.0 0
It can be clearly appreciated how the number of vm exits per second,
specially the ones related to notifications (kvm_fast_mmio and
kvm_msi_set_irq) is drastically lower.
Signed-off-by: Sergio Lopez <slp@redhat.com>
Add helpers to Vring and VhostUserSlaveReqHandler for EVENT_IDX, so
consumers of this crate can make use of this feature.
Signed-off-by: Sergio Lopez <slp@redhat.com>
Implement the newly added exit_event() method on the VhostUserBackend
trait to allow the backend to provide an EventFD for triggering an exit
of the worker thread.
Signed-off-by: Rob Bradford <robert.bradford@intel.com>
Adding the num_queues parameter for vhost-user-blk backend, which
can enable MQ support in the backend.
This patch has enabled the MQ support from handle_event, and the
vhost-user-backend crate will enable multiple threads to call this
handle_event to handle read/write operations.
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Split the basic launching functionality into its own function in the
newly added vhost_user_block crate.
Signed-off-by: Rob Bradford <robert.bradford@intel.com>
Extract the majority of the code that provides the vhost-user-block
backend into its own crate and port the binary to use it.
Signed-off-by: Rob Bradford <robert.bradford@intel.com>
