Currently, all blk requests are processed in notify_vq() which is in
the context of ioeventfd thread: ioeventfd__thread(). The processing
in notify_vq() may take a long time to complete.
We should make notify_vq() return as soon as possible, since all devices
are sharing the single ioeventfd thread. Otherwise, it will block other
device's notify_vq() being called and starve other devices.
In virtio net's notify_vq(), we simply signal the tx/rx handle thread
and return.
This patch makes virtio blk's notify_vq() just notify the blk thread
instead of doing the real hard read/write work. Tests show that the
overhead of the notification operations introduced by this patch is
small.
Signed-off-by: Asias He <asias.hejun@xxxxxxxxx>
---
tools/kvm/virtio/blk.c | 26 +++++++++++++++++++++++++-
1 files changed, 25 insertions(+), 1 deletions(-)
diff --git a/tools/kvm/virtio/blk.c b/tools/kvm/virtio/blk.c
index d1a0197..9d2f37e 100644
--- a/tools/kvm/virtio/blk.c
+++ b/tools/kvm/virtio/blk.c
@@ -51,6 +51,11 @@ struct blk_dev {
struct virt_queue vqs[NUM_VIRT_QUEUES];
struct blk_dev_req reqs[VIRTIO_BLK_QUEUE_SIZE];
+
+ pthread_t io_thread;
+ int io_efd;
+
+ struct kvm *kvm;
};
static LIST_HEAD(bdevs);
@@ -176,11 +181,26 @@ static int init_vq(struct kvm *kvm, void *dev, u32 vq, u32 pfn)
return 0;
}
+static void *virtio_blk_thread(void *dev)
+{
+ struct blk_dev *bdev = dev;
+ u64 data;
+
+ while (1) {
+ read(bdev->io_efd, &data, sizeof(u64));
+ virtio_blk_do_io(bdev->kvm, &bdev->vqs[0], bdev);
+ }
+
+ pthread_exit(NULL);
+ return NULL;
+}
+
static int notify_vq(struct kvm *kvm, void *dev, u32 vq)
{
struct blk_dev *bdev = dev;
+ u64 data = 1;
- virtio_blk_do_io(kvm, &bdev->vqs[vq], bdev);
+ write(bdev->io_efd, &data, sizeof(data));
return 0;
}
@@ -228,6 +248,8 @@ void virtio_blk__init(struct kvm *kvm, struct disk_image *disk)
.capacity = disk->size / SECTOR_SIZE,
.seg_max = DISK_SEG_MAX,
},
+ .io_efd = eventfd(0, 0),
+ .kvm = kvm,
};
virtio_trans_init(&bdev->vtrans, VIRTIO_PCI);
@@ -244,6 +266,8 @@ void virtio_blk__init(struct kvm *kvm, struct disk_image *disk)
disk_image__set_callback(bdev->disk, virtio_blk_complete);
+ pthread_create(&bdev->io_thread, NULL, virtio_blk_thread, bdev);
+
if (compat_id != -1)
compat_id = compat__add_message("virtio-blk device was not detected",
"While you have requested a virtio-blk device, "
--
1.7.7.3
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