在 2022/4/6 下午7:59, Michael S. Tsirkin 写道:
On Wed, Apr 06, 2022 at 04:35:36PM +0800, Jason Wang wrote:
This patch introduce
introduces
a new
new
virtio config ops to vring
callbacks. Transport specific method is required to call
synchornize_irq() on the IRQs. For the transport that doesn't provide
synchronize_vqs(), use synchornize_rcu() as a fallback.
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
include/linux/virtio_config.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index b341dd62aa4d..08b73d9bbff2 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -57,6 +57,8 @@ struct virtio_shm_region {
* include a NULL entry for vqs unused by driver
* Returns 0 on success or error status
* @del_vqs: free virtqueues found by find_vqs().
+ * @synchronize_vqs: synchronize with the virtqueue callbacks.
+ * vdev: the virtio_device
I think I prefer synchronize_callbacks
Ok, I will rename it.
* @get_features: get the array of feature bits for this device.
* vdev: the virtio_device
* Returns the first 64 feature bits (all we currently need).
@@ -89,6 +91,7 @@ struct virtio_config_ops {
const char * const names[], const bool *ctx,
struct irq_affinity *desc);
void (*del_vqs)(struct virtio_device *);
+ void (*synchronize_vqs)(struct virtio_device *);
u64 (*get_features)(struct virtio_device *vdev);
int (*finalize_features)(struct virtio_device *vdev);
const char *(*bus_name)(struct virtio_device *vdev);
@@ -217,6 +220,19 @@ int virtio_find_vqs_ctx(struct virtio_device *vdev, unsigned nvqs,
desc);
}
+/**
+ * virtio_synchronize_vqs - synchronize with virtqueue callbacks
+ * @vdev: the device
+ */
+static inline
+void virtio_synchronize_vqs(struct virtio_device *dev)
+{
+ if (dev->config->synchronize_vqs)
+ dev->config->synchronize_vqs(dev);
+ else
+ synchronize_rcu();
I am not sure about this fallback and the latency impact.
Unless each transport can implement their own synchronization routine,
we need something that can do best effort as fallback here.
Maybe synchronize_rcu_expedited is better here.
Not sure, it might lead IPIs and according to the
Documentation/RCU/checklist.rst:
"""
The expedited forms of these primitives have the same semantics
as the non-expedited forms, but expediting is both expensive and
(with the exception of synchronize_srcu_expedited()) unfriendly
to real-time workloads. Use of the expedited primitives should
be restricted to rare configuration-change operations that would
not normally be undertaken while a real-time workload is running.
However, real-time workloads can use rcupdate.rcu_normal kernel
boot parameter to completely disable expedited grace periods,
though this might have performance implications.
"""
It will be expensive for real time workloads.
Thanks
+}
+
/**
* virtio_device_ready - enable vq use in probe function
* @vdev: the device
--
2.25.1
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