Re: [PATCH v3 wireless-drivers 3/3] mt76: usb: do not always copy the first part of received frames

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Thu, Jun 13, 2019 at 11:43:13PM +0200, Lorenzo Bianconi wrote:
> Set usb buffer size taking into account skb_shared_info in order to
> not always copy the first part of received frames if A-MSDU is enabled
> for SG capable devices. Moreover align usb buffer size to max_ep
> boundaries and set buf_size to PAGE_SIZE even for sg case

I think this should not be applied to wirless-drivers, only first patch
that fix the bug and optimizations should be done in -next.

> +	int i, data_size;
>  
> +	data_size = rounddown(SKB_WITH_OVERHEAD(q->buf_size),
> +			      dev->usb.in_ep[MT_EP_IN_PKT_RX].max_packet);
>  	for (i = 0; i < nsgs; i++) {
>  		struct page *page;
>  		void *data;
> @@ -302,7 +304,7 @@ mt76u_fill_rx_sg(struct mt76_dev *dev, struct mt76_queue *q, struct urb *urb,
>  
>  		page = virt_to_head_page(data);
>  		offset = data - page_address(page);
> -		sg_set_page(&urb->sg[i], page, q->buf_size, offset);
> +		sg_set_page(&urb->sg[i], page, data_size, offset);
<snip>
> -	q->buf_size = dev->usb.sg_en ? MT_RX_BUF_SIZE : PAGE_SIZE;
>  	q->ndesc = MT_NUM_RX_ENTRIES;
> +	q->buf_size = PAGE_SIZE;
> +

This should be associated with decrease of MT_SG_MAX_SIZE to value that
is actually needed and currently this is 2 for 4k AMSDU.

However I don't think allocating 2 pages to avoid ieee80211 header and SNAP
copy is worth to do. For me best approach would be allocate 1 page for
4k AMSDU, 2 for 8k and 3 for 12k (still using sg, but without data_size
change to avoid 32B copying).

Stanislaw