From: Ming Lei <ming.lei@xxxxxxxxxxxxx> 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. Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx> --- drivers/usb/host/ehci-q.c | 18 ++++++++++++++++++ drivers/usb/host/ehci.h | 17 +++++++++++++++++ 2 files changed, 35 insertions(+), 0 deletions(-) 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 @@ static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh) 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 @@ static struct ehci_qh *qh_append_tds ( 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 cc7d337..313d9d6 100644 --- a/drivers/usb/host/ehci.h +++ b/drivers/usb/host/ehci.h @@ -738,6 +738,23 @@ static inline u32 hc32_to_cpup (const struct ehci_hcd *ehci, const __hc32 *x) #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 -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
