92 lines
4.1 KiB
Diff
92 lines
4.1 KiB
Diff
From: Stefan Hajnoczi <stefanha@redhat.com>
|
|
Date: Tue, 17 May 2022 09:27:45 +0100
|
|
Subject: [PATCH] virtio-scsi: don't waste CPU polling the event virtqueue
|
|
Content-type: text/plain
|
|
|
|
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>
|
|
(cherry picked from commit 38738f7dbbda90fbc161757b7f4be35b52205552)
|
|
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
|
|
---
|
|
hw/scsi/virtio-scsi-dataplane.c | 2 +-
|
|
hw/virtio/virtio.c | 13 +++++++++++++
|
|
include/hw/virtio/virtio.h | 1 +
|
|
3 files changed, 15 insertions(+), 1 deletion(-)
|
|
|
|
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
|
|
index 29575cbaf6..8bb6e6acfc 100644
|
|
--- a/hw/scsi/virtio-scsi-dataplane.c
|
|
+++ b/hw/scsi/virtio-scsi-dataplane.c
|
|
@@ -138,7 +138,7 @@ int virtio_scsi_dataplane_start(VirtIODevice *vdev)
|
|
|
|
aio_context_acquire(s->ctx);
|
|
virtio_queue_aio_attach_host_notifier(vs->ctrl_vq, s->ctx);
|
|
- virtio_queue_aio_attach_host_notifier(vs->event_vq, s->ctx);
|
|
+ virtio_queue_aio_attach_host_notifier_no_poll(vs->event_vq, s->ctx);
|
|
|
|
for (i = 0; i < vs->conf.num_queues; i++) {
|
|
virtio_queue_aio_attach_host_notifier(vs->cmd_vqs[i], s->ctx);
|
|
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
|
|
index 9d637e043e..67a873f54a 100644
|
|
--- a/hw/virtio/virtio.c
|
|
+++ b/hw/virtio/virtio.c
|
|
@@ -3534,6 +3534,19 @@ void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx)
|
|
virtio_queue_host_notifier_aio_poll_end);
|
|
}
|
|
|
|
+/*
|
|
+ * Same as virtio_queue_aio_attach_host_notifier() but without polling. Use
|
|
+ * this for rx virtqueues and similar cases where the virtqueue handler
|
|
+ * function does not pop all elements. When the virtqueue is left non-empty
|
|
+ * polling consumes CPU cycles and should not be used.
|
|
+ */
|
|
+void virtio_queue_aio_attach_host_notifier_no_poll(VirtQueue *vq, AioContext *ctx)
|
|
+{
|
|
+ aio_set_event_notifier(ctx, &vq->host_notifier, true,
|
|
+ virtio_queue_host_notifier_read,
|
|
+ NULL, NULL);
|
|
+}
|
|
+
|
|
void virtio_queue_aio_detach_host_notifier(VirtQueue *vq, AioContext *ctx)
|
|
{
|
|
aio_set_event_notifier(ctx, &vq->host_notifier, true, NULL, NULL, NULL);
|
|
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
|
|
index b31c4507f5..b62a35fdca 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);
|