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

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

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> 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.

ack, right. I think patch 2/3 and 3/3 can go directly in Felix's tree

> 
> > +	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.

MT_SG_MAX_SIZE is used even on tx side and I do not think we will end up with a
huge difference here

> 
> 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).

From my point of view it is better to avoid copying if it is possible. Are you
sure there is no difference?

Regards,
Lorenzo

> 
> Stanislaw

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