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virtio-fs: improved request latencies when Virtio queue is full

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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 <pgootzen@nvidia.com>
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Reviewed-by: Yoray Zack <yorayz@nvidia.com>
Message-Id: <20240517190435.152096-3-pgootzen@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Peter-Jan Gootzen 2024-05-17 21:04:35 +02:00 committed by Michael S. Tsirkin
parent 2106e1f444
commit 106e4df120
1 changed files with 19 additions and 15 deletions
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34
fs/fuse/virtio_fs.c
View File

@ -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);
}
}
@ -1375,8 +1381,6 @@ __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;
}
@ -1386,7 +1390,7 @@ __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;
}