usb: Add packet combining functions

Currently we only do pipelining for output endpoints, since to properly
support short-not-ok semantics we can only have one outstanding input
packet. Since the ehci and uhci controllers have a limited per td packet
size guests will split large input transfers to into multiple packets,
and since we don't pipeline these, this comes with a serious performance
penalty.

This patch adds helper functions to (re-)combine packets which belong to 1
transfer at the guest device-driver level into 1 large transger. This can be
used by (redirection) usb-devices to enable pipelining for input endpoints.

This patch will combine packets together until a transfer terminating packet
is encountered. A terminating packet is a packet which meets one or more of
the following conditions:
1) The packet size is *not* a multiple of the endpoint max packet size
2) The packet does *not* have its short-not-ok flag set
3) The packet has its interrupt-on-complete flag set

The short-not-ok flag of the combined packet is that of the terminating packet.
Multiple combined packets may be submitted to the device, if the combined
packets do not have their short-not-ok flag set, enabling true pipelining.

If a combined packet does have its short-not-ok flag set the queue will
wait with submitting further packets to the device until that packet has
completed.

Once enabled in the usb-redir and ehci code, this improves the speed (MB/s)
of a Linux guest reading from a USB mass storage device by a factor of
1.2 - 1.5.

And the main reason why I started working on this, when reading from a pl2303
USB<->serial converter, it combines the previous 4 packets submitted per
device-driver level read into 1 big read, reducing the number of packets / sec
by a factor 4, and it allows to have multiple reads outstanding. This allows
for much better latency tolerance without the pl2303's internal buffer
overflowing (which was happening at 115200 bps, without serial flow control).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 179 insertions, 0 deletions

diff --git a/hw/usb/combined-packet.c b/hw/usb/combined-packet.c
new file mode 100644
index 0000000000..652bf02628
--- /dev/null
+++ b/hw/usb/combined-packet.c
@@ -0,0 +1,179 @@
+/*
+ * QEMU USB packet combining code (for input pipelining)
+ *
+ * Copyright(c) 2012 Red Hat, Inc.
+ *
+ * Red Hat Authors:
+ * Hans de Goede <hdegoede@redhat.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or(at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+#include "qemu-common.h"
+#include "hw/usb.h"
+#include "iov.h"
+#include "trace.h"
+
+static void usb_combined_packet_add(USBCombinedPacket *combined, USBPacket *p)
+{
+    qemu_iovec_concat(&combined->iov, &p->iov, 0, p->iov.size);
+    QTAILQ_INSERT_TAIL(&combined->packets, p, combined_entry);
+    p->combined = combined;
+}
+
+static void usb_combined_packet_remove(USBCombinedPacket *combined,
+                                       USBPacket *p)
+{
+    assert(p->combined == combined);
+    p->combined = NULL;
+    QTAILQ_REMOVE(&combined->packets, p, combined_entry);
+}
+
+/* Also handles completion of non combined packets for pipelined input eps */
+void usb_combined_input_packet_complete(USBDevice *dev, USBPacket *p)
+{
+    USBCombinedPacket *combined = p->combined;
+    USBEndpoint *ep = p->ep;
+    USBPacket *next;
+    enum { completing, complete, leftover };
+    int result, state = completing;
+    bool short_not_ok;
+
+    if (combined == NULL) {
+        usb_packet_complete_one(dev, p);
+        goto leave;
+    }
+
+    assert(combined->first == p && p == QTAILQ_FIRST(&combined->packets));
+
+    result = combined->first->result;
+    short_not_ok = QTAILQ_LAST(&combined->packets, packets_head)->short_not_ok;
+
+    QTAILQ_FOREACH_SAFE(p, &combined->packets, combined_entry, next) {
+        if (state == completing) {
+            /* Distribute data over uncombined packets */
+            if (result >= p->iov.size) {
+                p->result = p->iov.size;
+            } else {
+                /* Send short or error packet to complete the transfer */
+                p->result = result;
+                state = complete;
+            }
+            p->short_not_ok = short_not_ok;
+            usb_combined_packet_remove(combined, p);
+            usb_packet_complete_one(dev, p);
+            result -= p->result;
+        } else {
+            /* Remove any leftover packets from the queue */
+            state = leftover;
+            p->result = USB_RET_REMOVE_FROM_QUEUE;
+            dev->port->ops->complete(dev->port, p);
+        }
+    }
+    /*
+     * If we had leftover packets the hcd driver will have cancelled them
+     * and usb_combined_packet_cancel has already freed combined!
+     */
+    if (state != leftover) {
+        g_free(combined);
+    }
+leave:
+    /* Check if there are packets in the queue waiting for our completion */
+    usb_ep_combine_input_packets(ep);
+}
+
+/* May only be called for combined packets! */
+void usb_combined_packet_cancel(USBDevice *dev, USBPacket *p)
+{
+    USBCombinedPacket *combined = p->combined;
+    assert(combined != NULL);
+
+    usb_combined_packet_remove(combined, p);
+    if (p == combined->first) {
+        usb_device_cancel_packet(dev, p);
+    }
+    if (QTAILQ_EMPTY(&combined->packets)) {
+        g_free(combined);
+    }
+}
+
+/*
+ * Large input transfers can get split into multiple input packets, this
+ * function recombines them, removing the short_not_ok checks which all but
+ * the last packet of such splits transfers have, thereby allowing input
+ * transfer pipelining (which we cannot do on short_not_ok transfers)
+ */
+void usb_ep_combine_input_packets(USBEndpoint *ep)
+{
+    USBPacket *p, *u, *next, *prev = NULL, *first = NULL;
+    USBPort *port = ep->dev->port;
+    int ret;
+
+    assert(ep->pipeline);
+    assert(ep->pid == USB_TOKEN_IN);
+
+    QTAILQ_FOREACH_SAFE(p, &ep->queue, queue, next) {
+        /* Empty the queue on a halt */
+        if (ep->halted) {
+            p->result = USB_RET_REMOVE_FROM_QUEUE;
+            port->ops->complete(port, p);
+            continue;
+        }
+
+        /* Skip packets already submitted to the device */
+        if (p->state == USB_PACKET_ASYNC) {
+            prev = p;
+            continue;
+        }
+        usb_packet_check_state(p, USB_PACKET_QUEUED);
+
+        /*
+         * If the previous (combined) packet has the short_not_ok flag set
+         * stop, as we must not submit packets to the device after a transfer
+         * ending with short_not_ok packet.
+         */
+        if (prev && prev->short_not_ok) {
+            break;
+        }
+
+        if (first) {
+            if (first->combined == NULL) {
+                USBCombinedPacket *combined = g_new0(USBCombinedPacket, 1);
+
+                combined->first = first;
+                QTAILQ_INIT(&combined->packets);
+                qemu_iovec_init(&combined->iov, 2);
+                usb_combined_packet_add(combined, first);
+            }
+            usb_combined_packet_add(first->combined, p);
+        } else {
+            first = p;
+        }
+
+        /* Is this packet the last one of a (combined) transfer? */
+        if ((p->iov.size % ep->max_packet_size) != 0 || !p->short_not_ok ||
+                next == NULL) {
+            ret = usb_device_handle_data(ep->dev, first);
+            assert(ret == USB_RET_ASYNC);
+            if (first->combined) {
+                QTAILQ_FOREACH(u, &first->combined->packets, combined_entry) {
+                    usb_packet_set_state(u, USB_PACKET_ASYNC);
+                }
+            } else {
+                usb_packet_set_state(first, USB_PACKET_ASYNC);
+            }
+            first = NULL;
+            prev = p;
+        }
+    }
+}