Hi again,
Felipe Balbi <balbi@xxxxxxxxxx> writes:
>>>> Enabling SG allows enabling GSO (generic segmentation offload) feature
>>>> of linux networking layer. This increases TCP throughput with NCM
>>>> on Cortex-A15+USB3380 based device from 300 Mbit/s to 1.1 Gbit/s.
>>>>
>>>> Signed-off-by: Jussi Kivilinna <jussi.kivilinna@xxxxxxxxxxx>
>>>
>>> this is AWESOME!! :-) But here's the thing, any chance we can build this
>>> in u_ether.c ? Also, NETIF_F_SG should be conditional on
>>> gadget->sg_supported so that we don't break UDCs that don't support
>>> sglists.
>>>
>>
>> Actually, no sglists are passed to UDC. Reason why this work
>> with minimal changes for NCM is that NCM does tx buffering
>> in its wrap function.. 'ncm_wrap_ntb' copies input skbuffs to
>> larger skbuff, so enabling SG is only matter of changing that
>> skbuff data copy from 'memcpy' to 'skb_copy_bits' (and changing
>> CRC calculation work with skbuff fragments). Since NCM already
>> does copying, SG can be enabled for NCM without extra overhead.
>
> aha, understood. Now what if we skip copying altogether? If we have an
> sg and a UDC that supports sg (gadget->sg_supported = 1), then we can
> avoid copying, right?
perhaps this is the crud of the change (still need to check for
sg_supported)?
diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index 5f562c1ec795..f3497cba32ec 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -235,7 +235,7 @@ rx_submit(struct eth_dev *dev, struct usb_request *req, gfp_t gfp_flags)
*/
skb_reserve(skb, NET_IP_ALIGN);
- req->buf = skb->data;
+ req->num_sgs = skb_to_sgvec(skb, req->sg, 0, skb->len);
req->length = size;
req->complete = rx_complete;
req->context = skb;
--
balbi
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