Currently, when the Virtio queue is full, a work item is scheduled
to execute in 1ms that retries adding the request to the queue.
This is a large amount of time on the scale on which a
virtio-fs device can operate. When using a DPU this is around
30-40us baseline without going to a remote server (4k, QD=1).
This patch changes the retrying behavior to immediately filling the
Virtio queue up again when a completion has been received.
This reduces the 99.9th percentile latencies in our tests by
60x and slightly increases the overall throughput, when using a
workload IO depth 2x the size of the Virtio queue and a
DPU-powered virtio-fs device (NVIDIA BlueField DPU).
Signed-off-by: Peter-Jan Gootzen <pgoot...@nvidia.com>
Reviewed-by: Max Gurtovoy <mgurto...@nvidia.com>
Reviewed-by: Yoray Zack <yor...@nvidia.com>
---
fs/fuse/virtio_fs.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 55126df202d6..fdeb7e34ec01 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -51,7 +51,7 @@ struct virtio_fs_vq {
struct work_struct done_work;
struct list_head queued_reqs;
struct list_head end_reqs; /* End these requests */
- struct delayed_work dispatch_work;
+ struct work_struct dispatch_work;
struct fuse_dev *fud;
bool connected;
long in_flight;
@@ -233,7 +233,7 @@ static void virtio_fs_drain_queue(struct virtio_fs_vq *fsvq)
}
flush_work(&fsvq->done_work);
- flush_delayed_work(&fsvq->dispatch_work);
+ flush_work(&fsvq->dispatch_work);
}
static void virtio_fs_drain_all_queues_locked(struct virtio_fs *fs)
@@ -408,6 +408,10 @@ static void virtio_fs_hiprio_done_work(struct work_struct
*work)
dec_in_flight_req(fsvq);
}
} while (!virtqueue_enable_cb(vq));
+
+ if (!list_empty(&fsvq->queued_reqs))
+ schedule_work(&fsvq->dispatch_work);
+
spin_unlock(&fsvq->lock);
}
@@ -415,7 +419,7 @@ static void virtio_fs_request_dispatch_work(struct
work_struct *work)
{
struct fuse_req *req;
struct virtio_fs_vq *fsvq = container_of(work, struct virtio_fs_vq,
- dispatch_work.work);
+ dispatch_work);
int ret;
pr_debug("virtio-fs: worker %s called.\n", __func__);
@@ -450,8 +454,6 @@ static void virtio_fs_request_dispatch_work(struct
work_struct *work)
if (ret == -ENOSPC) {
spin_lock(&fsvq->lock);
list_add_tail(&req->list, &fsvq->queued_reqs);
- schedule_delayed_work(&fsvq->dispatch_work,
- msecs_to_jiffies(1));
spin_unlock(&fsvq->lock);
return;
}
@@ -498,8 +500,6 @@ static int send_forget_request(struct virtio_fs_vq *fsvq,
pr_debug("virtio-fs: Could not queue FORGET: err=%d.
Will try later\n",
ret);
list_add_tail(&forget->list, &fsvq->queued_reqs);
- schedule_delayed_work(&fsvq->dispatch_work,
- msecs_to_jiffies(1));
if (!in_flight)
inc_in_flight_req(fsvq);
/* Queue is full */
@@ -531,7 +531,7 @@ static void virtio_fs_hiprio_dispatch_work(struct
work_struct *work)
{
struct virtio_fs_forget *forget;
struct virtio_fs_vq *fsvq = container_of(work, struct virtio_fs_vq,
- dispatch_work.work);
+ dispatch_work);
pr_debug("virtio-fs: worker %s called.\n", __func__);
while (1) {
spin_lock(&fsvq->lock);
@@ -709,6 +709,12 @@ static void virtio_fs_requests_done_work(struct
work_struct *work)
virtio_fs_request_complete(req, fsvq);
}
}
+
+ /* Try to push previously queued requests, as the queue might no longer
be full */
+ spin_lock(&fsvq->lock);
+ if (!list_empty(&fsvq->queued_reqs))
+ schedule_work(&fsvq->dispatch_work);
+ spin_unlock(&fsvq->lock);
}
static void virtio_fs_map_queues(struct virtio_device *vdev, struct virtio_fs
*fs)
@@ -770,12 +776,12 @@ static void virtio_fs_init_vq(struct virtio_fs_vq *fsvq,
char *name,
if (vq_type == VQ_REQUEST) {
INIT_WORK(&fsvq->done_work, virtio_fs_requests_done_work);
- INIT_DELAYED_WORK(&fsvq->dispatch_work,
- virtio_fs_request_dispatch_work);
+ INIT_WORK(&fsvq->dispatch_work,
+ virtio_fs_request_dispatch_work);
} else {
INIT_WORK(&fsvq->done_work, virtio_fs_hiprio_done_work);
- INIT_DELAYED_WORK(&fsvq->dispatch_work,
- virtio_fs_hiprio_dispatch_work);
+ INIT_WORK(&fsvq->dispatch_work,
+ virtio_fs_hiprio_dispatch_work);
}
}
@@ -1376,8 +1382,6 @@ __releases(fiq->lock)
spin_lock(&fsvq->lock);
list_add_tail(&req->list, &fsvq->queued_reqs);
inc_in_flight_req(fsvq);
- schedule_delayed_work(&fsvq->dispatch_work,
- msecs_to_jiffies(1));
spin_unlock(&fsvq->lock);
return;
}
@@ -1387,7 +1391,7 @@ __releases(fiq->lock)
/* Can't end request in submission context. Use a worker */
spin_lock(&fsvq->lock);
list_add_tail(&req->list, &fsvq->end_reqs);
- schedule_delayed_work(&fsvq->dispatch_work, 0);
+ schedule_work(&fsvq->dispatch_work);
spin_unlock(&fsvq->lock);
return;
}
--
2.34.1
