path: root/drivers/usb/host/ehci-q.c
diff options
authorAlan Stern <stern@rowland.harvard.edu>2013-10-11 11:29:13 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-10-11 16:45:43 -0700
commitd0ce5c6b9208c79fc725c578eebdeb5724faf17d (patch)
tree4b720313bb5b9e2d7c9392c25a12bca901e92136 /drivers/usb/host/ehci-q.c
parentffa0248e643175cea3887c7058916af53104d8e5 (diff)
USB: EHCI: use a bandwidth-allocation table
This patch significantly changes the scheduling code in ehci-hcd. Instead of calculating the current bandwidth utilization by trudging through the schedule and adding up the times used by the existing transfers, we will now maintain a table holding the time used for each of 64 microframes. This will drastically speed up the bandwidth computations. In addition, it eliminates a theoretical bug. An isochronous endpoint may have bandwidth reserved even at times when it has no transfers listed in the schedule. The table will keep track of the reserved bandwidth, whereas adding up entries in the schedule would miss it. As a corollary, we can keep bandwidth reserved for endpoints even when they aren't in active use. Eventually the bandwidth will be reserved when a new alternate setting is installed; for now the endpoint's reservation takes place when its first URB is submitted. A drawback of this approach is that transfers with an interval larger than 64 microframes will have to be charged for bandwidth as though the interval was 64. In practice this shouldn't matter much; transfers with longer intervals tend to be rather short anyway (things like hubs or HID devices). Another minor drawback is that we will keep track of two different period and phase values: the actual ones and the ones used for bandwidth allocation (which are limited to 64). This adds only a small amount of overhead: 3 bytes for each endpoint. The patch also adds a new debugfs file named "bandwidth" to display the information stored in the new table. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/host/ehci-q.c')
1 files changed, 19 insertions, 0 deletions
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 9bfaa21707bd..db05bd8ee9d5 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -797,6 +797,8 @@ qh_make (
* For control/bulk requests, the HC or TT handles these.
if (type == PIPE_INTERRUPT) {
+ unsigned tmp;
qh->ps.usecs = NS_TO_US(usb_calc_bus_time(USB_SPEED_HIGH,
is_input, 0,
hb_mult(maxp) * max_packet(maxp)));
@@ -816,6 +818,14 @@ qh_make (
urb->interval = ehci->periodic_size << 3;
qh->ps.period = urb->interval >> 3;
+ /* period for bandwidth allocation */
+ tmp = min_t(unsigned, EHCI_BANDWIDTH_SIZE,
+ 1 << (urb->ep->desc.bInterval - 1));
+ /* Allow urb->interval to override */
+ qh->ps.bw_uperiod = min_t(unsigned, tmp, urb->interval);
+ qh->ps.bw_period = qh->ps.bw_uperiod >> 3;
} else {
int think_time;
@@ -839,6 +849,15 @@ qh_make (
if (urb->interval > ehci->periodic_size)
urb->interval = ehci->periodic_size;
qh->ps.period = urb->interval;
+ /* period for bandwidth allocation */
+ tmp = min_t(unsigned, EHCI_BANDWIDTH_FRAMES,
+ urb->ep->desc.bInterval);
+ tmp = rounddown_pow_of_two(tmp);
+ /* Allow urb->interval to override */
+ qh->ps.bw_period = min_t(unsigned, tmp, urb->interval);
+ qh->ps.bw_uperiod = qh->ps.bw_period << 3;