On Thu, Mar 24, 2022 at 06:48:05AM -0400, Michael S. Tsirkin wrote:
On Thu, Mar 24, 2022 at 04:40:02PM +0800, Jason Wang wrote:
From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
This avoids setting DRIVER_OK twice for those drivers that call
virtio_device_ready() in the .restore
Is this trying to say it's faster?
Nope, I mean, when I wrote the original version, I meant to do the same
things that we do in virtio_dev_probe() where we called
virtio_device_ready() which not only set the state, but also called
.enable_cbs callback.
Was this a side effect and maybe more compliant with the spec?
If yes this one looks like a red herring. Yes we skip a write but we
replace it with a read which is not better performance-wise.
If we want to optimize this, it is better to just do that inside
virtio_add_status:
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 75c8d560bbd3..cd943c31bdbb 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -161,8 +161,14 @@ static void virtio_config_enable(struct virtio_device *dev)
void virtio_add_status(struct virtio_device *dev, unsigned int status)
{
+ unsigned int device_status;
+
might_sleep();
- dev->config->set_status(dev, dev->config->get_status(dev) | status);
+
+ device_status = dev->config->get_status(dev);
+
+ if (status & ~device_status)
+ dev->config->set_status(dev, device_status | status);
}
EXPORT_SYMBOL_GPL(virtio_add_status);
Could there be a case where we want to set the status again even though
the device tells us it's already set?
I think not, so I guess it's okay.
and it will allows us to do
extension on virtio_device_ready() without duplicating codes.
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
drivers/virtio/virtio.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 22f15f444f75..75c8d560bbd3 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -526,8 +526,9 @@ int virtio_device_restore(struct virtio_device *dev)
goto err;
}
- /* Finally, tell the device we're all set */
- virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
+ /* If restore didn't do it, mark device DRIVER_OK ourselves. */
I preferred the original comment, it said why we are doing this,
new one repeats what code is doing.
I agree, copy & paste from virtio_dev_probe().
Jason can you fix this patch or should I resend?
Thanks,
Stefano
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