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| author | Stefan Hajnoczi <stefanha@redhat.com> | 2022-04-27 15:35:37 +0100 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2022-05-09 10:45:04 +0100 |
| commit | 38738f7dbbda90fbc161757b7f4be35b52205552 (patch) | |
| tree | 988e4b58b3216bc1107759359931a47dca2324d6 /include/hw | |
| parent | 2f743ef6366c2df4ef51ef3ae318138cdc0125ab (diff) | |
| download | qemu-38738f7dbbda90fbc161757b7f4be35b52205552.zip qemu-38738f7dbbda90fbc161757b7f4be35b52205552.tar.gz qemu-38738f7dbbda90fbc161757b7f4be35b52205552.tar.bz2 | |
virtio-scsi: don't waste CPU polling the event virtqueue
The virtio-scsi event virtqueue is not emptied by its handler function.
This is typical for rx virtqueues where the device uses buffers when
some event occurs (e.g. a packet is received, an error condition
happens, etc).
Polling non-empty virtqueues wastes CPU cycles. We are not waiting for
new buffers to become available, we are waiting for an event to occur,
so it's a misuse of CPU resources to poll for buffers.
Introduce the new virtio_queue_aio_attach_host_notifier_no_poll() API,
which is identical to virtio_queue_aio_attach_host_notifier() except
that it does not poll the virtqueue.
Before this patch the following command-line consumed 100% CPU in the
IOThread polling and calling virtio_scsi_handle_event():
$ qemu-system-x86_64 -M accel=kvm -m 1G -cpu host \
--object iothread,id=iothread0 \
--device virtio-scsi-pci,iothread=iothread0 \
--blockdev file,filename=test.img,aio=native,cache.direct=on,node-name=drive0 \
--device scsi-hd,drive=drive0
After this patch CPU is no longer wasted.
Reported-by: Nir Soffer <nsoffer@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Nir Soffer <nsoffer@redhat.com>
Message-id: 20220427143541.119567-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'include/hw')
| -rw-r--r-- | include/hw/virtio/virtio.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h index b31c450..b62a35f 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -317,6 +317,7 @@ EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq); void virtio_queue_set_host_notifier_enabled(VirtQueue *vq, bool enabled); void virtio_queue_host_notifier_read(EventNotifier *n); void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx); +void virtio_queue_aio_attach_host_notifier_no_poll(VirtQueue *vq, AioContext *ctx); void virtio_queue_aio_detach_host_notifier(VirtQueue *vq, AioContext *ctx); VirtQueue *virtio_vector_first_queue(VirtIODevice *vdev, uint16_t vector); VirtQueue *virtio_vector_next_queue(VirtQueue *vq); |