[Qemu-devel] [PATCH 12/32] uhci: Fix 1 ms delay in interrupt reporting to the guest

[Gerd Hoffmann <kraxel@redhat.com>]

From: Hans de Goede <hdegoede@redhat.com>

Re-arrange how we process frames / increase frnum / report pending interrupts,
to avoid a 1 ms delay in interrupt reporting to the guest. This increases
the packet throughput for cases where the guest submits a single packet,
then waits for its completion then re-submits from 500 pkts / sec to
1000 pkts / sec. This impacts for example the use of redirected / virtual
usb to serial convertors.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/usb/hcd-uhci.c |   24 +++++++++++++-----------
 1 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/hw/usb/hcd-uhci.c b/hw/usb/hcd-uhci.c
index 2af754b..5685b9f 100644
--- a/hw/usb/hcd-uhci.c
+++ b/hw/usb/hcd-uhci.c
@@ -1191,17 +1191,7 @@ static void uhci_frame_timer(void *opaque)
         return;
     }
 
-    /* Complete the previous frame */
-    if (s->pending_int_mask) {
-        s->status2 |= s->pending_int_mask;
-        s->status  |= UHCI_STS_USBINT;
-        uhci_update_irq(s);
-    }
-    s->pending_int_mask = 0;
-
-    /* Start new frame */
-    s->frnum = (s->frnum + 1) & 0x7ff;
-
+    /* Process the current frame */
     trace_usb_uhci_frame_start(s->frnum);
 
     uhci_async_validate_begin(s);
@@ -1210,6 +1200,18 @@ static void uhci_frame_timer(void *opaque)
 
     uhci_async_validate_end(s);
 
+    /* The uhci spec says frnum reflects the frame currently being processed,
+     * and the guest must look at frnum - 1 on interrupt, so inc frnum now */
+    s->frnum = (s->frnum + 1) & 0x7ff;
+
+    /* Complete the previous frame */
+    if (s->pending_int_mask) {
+        s->status2 |= s->pending_int_mask;
+        s->status  |= UHCI_STS_USBINT;
+        uhci_update_irq(s);
+    }
+    s->pending_int_mask = 0;
+
     qemu_mod_timer(s->frame_timer, s->expire_time);
 }
 
-- 
1.7.1