usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP
This patch introduces the helper of ehci_sync_mem to flush
qtd/qh into memory immediately on some ARM, so that HC can
see the up-to-date qtd/qh descriptor asap.
This patch fixs one performance bug on ARM Cortex A9 dual core
platform, which has been reported on quite a few ARM machines
(OMAP4, Tegra 2, snowball...), see details from link of
https://bugs.launchpad.net/bugs/709245.
The patch has been tested ok on OMAP4 panda A1 board, and the
performance of 'dd' over usb mass storage can be increased from
4~5MB/sec to 14~16MB/sec after applying this patch.
Change-Id: I7994c58a1001c7f46f13e09420328a3916bbfcef
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 0917e3a..2719879 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -995,6 +995,12 @@
head->qh_next.qh = qh;
head->hw->hw_next = dma;
+ /*
+ * flush qh descriptor into memory immediately,
+ * see comments in qh_append_tds.
+ * */
+ ehci_sync_mem();
+
qh_get(qh);
qh->xacterrs = 0;
qh->qh_state = QH_STATE_LINKED;
@@ -1082,6 +1088,18 @@
wmb ();
dummy->hw_token = token;
+ /*
+ * Writing to dma coherent buffer on ARM may
+ * be delayed to reach memory, so HC may not see
+ * hw_token of dummy qtd in time, which can cause
+ * the qtd transaction to be executed very late,
+ * and degrade performance a lot. ehci_sync_mem
+ * is added to flush 'token' immediatelly into
+ * memory, so that ehci can execute the transaction
+ * ASAP.
+ * */
+ ehci_sync_mem();
+
urb->hcpriv = qh_get (qh);
}
}
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index 989e0a8..9706c2b 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -736,6 +736,23 @@
#endif
+/*
+ * Writing to dma coherent memory on ARM may be delayed via L2
+ * writing buffer, so introduce the helper which can flush L2 writing
+ * buffer into memory immediately, especially used to flush ehci
+ * descriptor to memory.
+ * */
+#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
+static inline void ehci_sync_mem()
+{
+ mb();
+}
+#else
+static inline void ehci_sync_mem()
+{
+}
+#endif
+
/*-------------------------------------------------------------------------*/
#ifndef DEBUG