On Wed, 31 Aug 2011 [email protected] wrote:
> From: Ming Lei <[email protected]>
>
> 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 <[email protected]>
> Cc: Russell King <[email protected]>
> Signed-off-by: Ming Lei <[email protected]>
> ---
> 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.
> + * */
Comments are supposed to look like this:
/*
* Blah blah blah
* blah blah blah
*/
> + 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.
> + * */
Here too.
> + 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.
> + * */
And here.
> +#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
> +static inline void ehci_sync_mem()
> +{
> + mb();
> +}
> +#else
> +static inline void ehci_sync_mem()
> +{
> +}
> +#endif
> +
Except for the formatting of the comments, this is fine. When you fix
up the comments, you can add:
Signed-off-by: Alan Stern <[email protected]>
Alan Stern
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