On Sat, 3 Feb 2007, Oliver Neukum wrote:
> If you want simplicity, I'd suggest serialization. kmalloc for 4 bytes
> is overkill. I think it is even faster if we block on the cases there's
> a collision that go through kmalloc/kfree each time.
On the other hand, the same routine calls usb_control_message() which does
two kmallocs: one for the URB and one for the usb_ctrlrequest structure.
Adding a third for the buffer wouldn't be so bad.
Or we could pre-allocate everything; the ctrlrequest could even share the
same cacheline as the I/O buffer. But most hubs are idle almost all the
time, and it doesn't seem worthwhile to allocate permanently one URB per
hub if it will hardly ever be used.
Prakash, here's an alternative patch. It should work just as well as the
previous one (don't try to apply them both!).
Alan Stern
Index: usb-2.6/drivers/usb/core/hub.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/hub.c
+++ usb-2.6/drivers/usb/core/hub.c
@@ -44,6 +44,7 @@ struct usb_hub {
struct usb_hub_status hub;
struct usb_port_status port;
} *status; /* buffer for status reports */
+ struct mutex status_mutex; /* for the status buffer */
int error; /* last reported error */
int nerrors; /* track consecutive errors */
@@ -545,6 +546,7 @@ static int hub_hub_status(struct usb_hub
{
int ret;
+ mutex_lock(&hub->status_mutex);
ret = get_hub_status(hub->hdev, &hub->status->hub);
if (ret < 0)
dev_err (hub->intfdev,
@@ -554,6 +556,7 @@ static int hub_hub_status(struct usb_hub
*change = le16_to_cpu(hub->status->hub.wHubChange);
ret = 0;
}
+ mutex_unlock(&hub->status_mutex);
return ret;
}
@@ -627,6 +630,7 @@ static int hub_configure(struct usb_hub
ret = -ENOMEM;
goto fail;
}
+ mutex_init(&hub->status_mutex);
hub->descriptor = kmalloc(sizeof(*hub->descriptor), GFP_KERNEL);
if (!hub->descriptor) {
@@ -1423,6 +1427,7 @@ static int hub_port_status(struct usb_hu
{
int ret;
+ mutex_lock(&hub->status_mutex);
ret = get_port_status(hub->hdev, port1, &hub->status->port);
if (ret < 4) {
dev_err (hub->intfdev,
@@ -1434,6 +1439,7 @@ static int hub_port_status(struct usb_hu
*change = le16_to_cpu(hub->status->port.wPortChange);
ret = 0;
}
+ mutex_unlock(&hub->status_mutex);
return ret;
}
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