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Date:   Fri, 14 Jun 2019 13:04:43 +0200
From:   Stanislaw Gruszka <sgruszka@redhat.com>
To:     Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Cc:     Lorenzo Bianconi <lorenzo@kernel.org>, kvalo@codeaurora.org,
        linux-wireless@vger.kernel.org, nbd@nbd.name
Subject: Re: [PATCH v3 wireless-drivers 3/3] mt76: usb: do not always copy
 the first part of received frames
Message-ID: <20190614110442.GA17298@redhat.com>
References: <cover.1560461404.git.lorenzo@kernel.org>
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 <20190614075303.GB3395@redhat.com>
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On Fri, Jun 14, 2019 at 12:22:48PM +0200, Lorenzo Bianconi wrote:
> > 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

So use different value as argument for mt76u_fill_rx_sg() in
mt76u_rx_urb_alloc(). After changing buf_size to PAGE_SIZE we will
allocate 8 pages per rx queue entry, but only 2 pages will be used
(with data_size change, 1 without data_size change). Or I'm wrong?

> > 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?

I do not understand what you mean by difference here.

Stanislaw