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Date:   Fri, 14 Jun 2019 14:46:36 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To:     Stanislaw Gruszka <sgruszka@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
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References: <cover.1560461404.git.lorenzo@kernel.org>
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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 enab=
led
> > > > for SG capable devices. Moreover align usb buffer size to max_ep
> > > > boundaries and set buf_size to PAGE_SIZE even for sg case
> > >=20
> > > I think this should not be applied to wirless-drivers, only first pat=
ch
> > > that fix the bug and optimizations should be done in -next.
> >=20
> > ack, right. I think patch 2/3 and 3/3 can go directly in Felix's tree
> >=20
> > >=20
> > > > +	int i, data_size;
> > > > =20
> > > > +	data_size =3D rounddown(SKB_WITH_OVERHEAD(q->buf_size),
> > > > +			      dev->usb.in_ep[MT_EP_IN_PKT_RX].max_packet);
> > > >  	for (i =3D 0; i < nsgs; i++) {
> > > >  		struct page *page;
> > > >  		void *data;
> > > > @@ -302,7 +304,7 @@ mt76u_fill_rx_sg(struct mt76_dev *dev, struct m=
t76_queue *q, struct urb *urb,
> > > > =20
> > > >  		page =3D virt_to_head_page(data);
> > > >  		offset =3D 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 =3D dev->usb.sg_en ? MT_RX_BUF_SIZE : PAGE_SIZE;
> > > >  	q->ndesc =3D MT_NUM_RX_ENTRIES;
> > > > +	q->buf_size =3D PAGE_SIZE;
> > > > +
> > >=20
> > > This should be associated with decrease of MT_SG_MAX_SIZE to value th=
at
> > > is actually needed and currently this is 2 for 4k AMSDU.
> >=20
> > MT_SG_MAX_SIZE is used even on tx side and I do not think we will end u=
p with a
> > huge difference here
>=20
> 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?

yes, it is right (we will use two pages with data_size change). Maybe bette=
r to
use 4 pages for each rx queue entry? (otherwise we will probably change it =
in
the future)

>=20
> > > However I don't think allocating 2 pages to avoid ieee80211 header an=
d 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_si=
ze
> > > change to avoid 32B copying).
> >=20
> > From my point of view it is better to avoid copying if it is possible. =
Are you
> > sure there is no difference?
>=20
> I do not understand what you mean by difference here.

tpt differences, not sure if there are any

Regards,
Lorenzo

>=20
> Stanislaw

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