[PATCH v3 wireless-drivers 0/3] mt76: usb: fix A-MSDU support

[PATCH v3 wireless-drivers 0/3] mt76: usb: fix A-MSDU support

[Lorenzo Bianconi]

Reallocate the skb if there is no enough space to manage the AMSDU rx packets.
Do not always copy the first part of received frames if A-MSDU is enabled
for SG capable devices

Changes since v2:
- simplify mt76u_build_rx_skb
- add patch 2/3: mt76u: introduce mt76u_ep data structure
- align usb buffer size to usb max endpoint length
- set buf_size to PAGE_SIZE even for sg case

Changes since v1:
- do not allocate multiple page buffers but rely on fragmented skbs
  if there is no enough space to manage the AMSDU rx packets

Lorenzo Bianconi (3):
  mt76: usb: fix rx A-MSDU support
  mt76: mt76u: introduce mt76u_ep data structure
  mt76: usb: do not always copy the first part of received frames

 drivers/net/wireless/mediatek/mt76/mt76.h | 17 +++--
 drivers/net/wireless/mediatek/mt76/usb.c  | 75 +++++++++++++++++------
 2 files changed, 67 insertions(+), 25 deletions(-)

-- 
2.21.0

[PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Lorenzo Bianconi]

Commit f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes
for rx") breaks A-MSDU support. When A-MSDU is enable the device can
receive frames up to q->buf_size but they will be discarded in
mt76u_process_rx_entry since there is no enough room for
skb_shared_info. Fix the issue reallocating the skb and copying in the
linear area the first 128B of the received frames and in the frag_list
the remaining part.

Fixes: f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes for rx")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/wireless/mediatek/mt76/mt76.h |  1 +
 drivers/net/wireless/mediatek/mt76/usb.c  | 49 ++++++++++++++++++-----
 2 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
index 8ecbf81a906f..889b76deb703 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76.h
+++ b/drivers/net/wireless/mediatek/mt76/mt76.h
@@ -30,6 +30,7 @@
 #define MT_TX_RING_SIZE     256
 #define MT_MCU_RING_SIZE    32
 #define MT_RX_BUF_SIZE      2048
+#define MT_SKB_HEAD_LEN     128
 
 struct mt76_dev;
 struct mt76_wcid;
diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
index bbaa1365bbda..12d60d31cb51 100644
--- a/drivers/net/wireless/mediatek/mt76/usb.c
+++ b/drivers/net/wireless/mediatek/mt76/usb.c
@@ -429,6 +429,45 @@ static int mt76u_get_rx_entry_len(u8 *data, u32 data_len)
 	return dma_len;
 }
 
+static struct sk_buff *
+mt76u_build_rx_skb(u8 *data, int len, int buf_size)
+{
+	struct sk_buff *skb;
+
+	if (SKB_WITH_OVERHEAD(buf_size) < MT_DMA_HDR_LEN + len) {
+		struct page *page;
+		int offset;
+
+		/* slow path, not enough space for data and
+		 * skb_shared_info
+		 */
+		skb = alloc_skb(MT_SKB_HEAD_LEN, GFP_ATOMIC);
+		if (!skb)
+			return NULL;
+
+		skb_put_data(skb, data + MT_DMA_HDR_LEN, MT_SKB_HEAD_LEN);
+		data += (MT_SKB_HEAD_LEN + MT_DMA_HDR_LEN);
+		page = virt_to_head_page(data);
+		offset = data - (u8 *)page_address(page);
+
+		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
+				page, offset, len - MT_SKB_HEAD_LEN,
+				buf_size);
+
+		return skb;
+	}
+
+	/* fast path */
+	skb = build_skb(data, buf_size);
+	if (!skb)
+		return NULL;
+
+	skb_reserve(skb, MT_DMA_HDR_LEN);
+	__skb_put(skb, len);
+
+	return skb;
+}
+
 static int
 mt76u_process_rx_entry(struct mt76_dev *dev, struct urb *urb)
 {
@@ -446,19 +485,11 @@ mt76u_process_rx_entry(struct mt76_dev *dev, struct urb *urb)
 		return 0;
 
 	data_len = min_t(int, len, data_len - MT_DMA_HDR_LEN);
-	if (MT_DMA_HDR_LEN + data_len > SKB_WITH_OVERHEAD(q->buf_size)) {
-		dev_err_ratelimited(dev->dev, "rx data too big %d\n", data_len);
-		return 0;
-	}
-
-	skb = build_skb(data, q->buf_size);
+	skb = mt76u_build_rx_skb(data, data_len, q->buf_size);
 	if (!skb)
 		return 0;
 
-	skb_reserve(skb, MT_DMA_HDR_LEN);
-	__skb_put(skb, data_len);
 	len -= data_len;
-
 	while (len > 0 && nsgs < urb->num_sgs) {
 		data_len = min_t(int, len, urb->sg[nsgs].length);
 		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
-- 
2.21.0

[PATCH v3 wireless-drivers 2/3] mt76: mt76u: introduce mt76u_ep data structure

[Lorenzo Bianconi]

Introduce mt76u_ep data structure as a container for usb endpoint info.
This is a preliminary patch to compute proper usb buffer size and avoid
always copy the first part of received frames

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/wireless/mediatek/mt76/mt76.h | 16 ++++++++++------
 drivers/net/wireless/mediatek/mt76/usb.c  | 15 +++++++++------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
index 889b76deb703..1c51d6d48e60 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76.h
+++ b/drivers/net/wireless/mediatek/mt76/mt76.h
@@ -382,6 +382,11 @@ enum mt76u_out_ep {
 	__MT_EP_OUT_MAX,
 };
 
+struct mt76u_ep {
+	u16 max_packet;
+	u8 ep;
+};
+
 #define MT_SG_MAX_SIZE		8
 #define MT_NUM_TX_ENTRIES	256
 #define MT_NUM_RX_ENTRIES	128
@@ -393,10 +398,8 @@ struct mt76_usb {
 	struct tasklet_struct rx_tasklet;
 	struct delayed_work stat_work;
 
-	u8 out_ep[__MT_EP_OUT_MAX];
-	u16 out_max_packet;
-	u8 in_ep[__MT_EP_IN_MAX];
-	u16 in_max_packet;
+	struct mt76u_ep out_ep[__MT_EP_OUT_MAX];
+	struct mt76u_ep in_ep[__MT_EP_IN_MAX];
 	bool sg_en;
 
 	struct mt76u_mcu {
@@ -786,9 +789,10 @@ mt76u_bulk_msg(struct mt76_dev *dev, void *data, int len, int *actual_len,
 	unsigned int pipe;
 
 	if (actual_len)
-		pipe = usb_rcvbulkpipe(udev, usb->in_ep[MT_EP_IN_CMD_RESP]);
+		pipe = usb_rcvbulkpipe(udev, usb->in_ep[MT_EP_IN_CMD_RESP].ep);
 	else
-		pipe = usb_sndbulkpipe(udev, usb->out_ep[MT_EP_OUT_INBAND_CMD]);
+		pipe = usb_sndbulkpipe(udev,
+				       usb->out_ep[MT_EP_OUT_INBAND_CMD].ep);
 
 	return usb_bulk_msg(udev, pipe, data, len, actual_len, timeout);
 }
diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
index 12d60d31cb51..1ee54a9b302e 100644
--- a/drivers/net/wireless/mediatek/mt76/usb.c
+++ b/drivers/net/wireless/mediatek/mt76/usb.c
@@ -260,19 +260,22 @@ mt76u_set_endpoints(struct usb_interface *intf,
 	struct usb_host_interface *intf_desc = intf->cur_altsetting;
 	struct usb_endpoint_descriptor *ep_desc;
 	int i, in_ep = 0, out_ep = 0;
+	struct mt76u_ep *ep;
 
 	for (i = 0; i < intf_desc->desc.bNumEndpoints; i++) {
 		ep_desc = &intf_desc->endpoint[i].desc;
 
 		if (usb_endpoint_is_bulk_in(ep_desc) &&
 		    in_ep < __MT_EP_IN_MAX) {
-			usb->in_ep[in_ep] = usb_endpoint_num(ep_desc);
-			usb->in_max_packet = usb_endpoint_maxp(ep_desc);
+			ep = &usb->in_ep[in_ep];
+			ep->max_packet = usb_endpoint_maxp(ep_desc);
+			ep->ep = usb_endpoint_num(ep_desc);
 			in_ep++;
 		} else if (usb_endpoint_is_bulk_out(ep_desc) &&
 			   out_ep < __MT_EP_OUT_MAX) {
-			usb->out_ep[out_ep] = usb_endpoint_num(ep_desc);
-			usb->out_max_packet = usb_endpoint_maxp(ep_desc);
+			ep = &usb->out_ep[out_ep];
+			ep->max_packet = usb_endpoint_maxp(ep_desc);
+			ep->ep = usb_endpoint_num(ep_desc);
 			out_ep++;
 		}
 	}
@@ -386,9 +389,9 @@ mt76u_fill_bulk_urb(struct mt76_dev *dev, int dir, int index,
 	unsigned int pipe;
 
 	if (dir == USB_DIR_IN)
-		pipe = usb_rcvbulkpipe(udev, dev->usb.in_ep[index]);
+		pipe = usb_rcvbulkpipe(udev, dev->usb.in_ep[index].ep);
 	else
-		pipe = usb_sndbulkpipe(udev, dev->usb.out_ep[index]);
+		pipe = usb_sndbulkpipe(udev, dev->usb.out_ep[index].ep);
 
 	urb->dev = udev;
 	urb->pipe = pipe;
-- 
2.21.0

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

[Lorenzo Bianconi]

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

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/wireless/mediatek/mt76/usb.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
index 1ee54a9b302e..2ee3f8fa1483 100644
--- a/drivers/net/wireless/mediatek/mt76/usb.c
+++ b/drivers/net/wireless/mediatek/mt76/usb.c
@@ -289,8 +289,10 @@ static int
 mt76u_fill_rx_sg(struct mt76_dev *dev, struct mt76_queue *q, struct urb *urb,
 		 int nsgs, gfp_t gfp)
 {
-	int i;
+	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);
 	}
 
 	if (i < nsgs) {
@@ -314,7 +316,7 @@ mt76u_fill_rx_sg(struct mt76_dev *dev, struct mt76_queue *q, struct urb *urb,
 	}
 
 	urb->num_sgs = max_t(int, i, urb->num_sgs);
-	urb->transfer_buffer_length = urb->num_sgs * q->buf_size,
+	urb->transfer_buffer_length = urb->num_sgs * data_size;
 	sg_init_marker(urb->sg, urb->num_sgs);
 
 	return i ? : -ENOMEM;
@@ -611,8 +613,9 @@ static int mt76u_alloc_rx(struct mt76_dev *dev)
 	if (!q->entry)
 		return -ENOMEM;
 
-	q->buf_size = dev->usb.sg_en ? MT_RX_BUF_SIZE : PAGE_SIZE;
 	q->ndesc = MT_NUM_RX_ENTRIES;
+	q->buf_size = PAGE_SIZE;
+
 	for (i = 0; i < q->ndesc; i++) {
 		err = mt76u_rx_urb_alloc(dev, &q->entry[i]);
 		if (err < 0)
-- 
2.21.0

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Stanislaw Gruszka]

On Thu, Jun 13, 2019 at 11:43:11PM +0200, Lorenzo Bianconi wrote:
> Commit f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes
> for rx") breaks A-MSDU support. When A-MSDU is enable the device can
> receive frames up to q->buf_size but they will be discarded in
> mt76u_process_rx_entry since there is no enough room for
> skb_shared_info. Fix the issue reallocating the skb and copying in the
> linear area the first 128B of the received frames and in the frag_list
> the remaining part.
> 
> Fixes: f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes for rx")
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
>  drivers/net/wireless/mediatek/mt76/mt76.h |  1 +
>  drivers/net/wireless/mediatek/mt76/usb.c  | 49 ++++++++++++++++++-----
>  2 files changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> index 8ecbf81a906f..889b76deb703 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> @@ -30,6 +30,7 @@
>  #define MT_TX_RING_SIZE     256
>  #define MT_MCU_RING_SIZE    32
>  #define MT_RX_BUF_SIZE      2048
> +#define MT_SKB_HEAD_LEN     128
>  
>  struct mt76_dev;
>  struct mt76_wcid;
> diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> index bbaa1365bbda..12d60d31cb51 100644
> --- a/drivers/net/wireless/mediatek/mt76/usb.c
> +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> @@ -429,6 +429,45 @@ static int mt76u_get_rx_entry_len(u8 *data, u32 data_len)
>  	return dma_len;
>  }
>  
> +static struct sk_buff *
> +mt76u_build_rx_skb(u8 *data, int len, int buf_size)
> +{
> +	struct sk_buff *skb;
> +
> +	if (SKB_WITH_OVERHEAD(buf_size) < MT_DMA_HDR_LEN + len) {
> +		struct page *page;
> +		int offset;
> +
> +		/* slow path, not enough space for data and
> +		 * skb_shared_info
> +		 */
> +		skb = alloc_skb(MT_SKB_HEAD_LEN, GFP_ATOMIC);
> +		if (!skb)
> +			return NULL;
> +
> +		skb_put_data(skb, data + MT_DMA_HDR_LEN, MT_SKB_HEAD_LEN);

I looked how rx amsdu is processed in mac80211 and it is decomposed and
copied into newly allocated individual skb's, see ieee80211_amsdu_to_8023s()

So copy L3 & L4 headers doesn't do anything good here, actually seems to
be better to have them in frag as __ieee80211_amsdu_copy_frag() do some
magic to avid copy.

Stanislaw

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

[Stanislaw Gruszka]

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

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Lorenzo Bianconi]

[-- Attachment #1: Type: text/plain, Size: 3272 bytes --]

> On Thu, Jun 13, 2019 at 11:43:11PM +0200, Lorenzo Bianconi wrote:
> > Commit f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes
> > for rx") breaks A-MSDU support. When A-MSDU is enable the device can
> > receive frames up to q->buf_size but they will be discarded in
> > mt76u_process_rx_entry since there is no enough room for
> > skb_shared_info. Fix the issue reallocating the skb and copying in the
> > linear area the first 128B of the received frames and in the frag_list
> > the remaining part.
> > 
> > Fixes: f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes for rx")
> > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > ---
> >  drivers/net/wireless/mediatek/mt76/mt76.h |  1 +
> >  drivers/net/wireless/mediatek/mt76/usb.c  | 49 ++++++++++++++++++-----
> >  2 files changed, 41 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> > index 8ecbf81a906f..889b76deb703 100644
> > --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> > +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> > @@ -30,6 +30,7 @@
> >  #define MT_TX_RING_SIZE     256
> >  #define MT_MCU_RING_SIZE    32
> >  #define MT_RX_BUF_SIZE      2048
> > +#define MT_SKB_HEAD_LEN     128
> >  
> >  struct mt76_dev;
> >  struct mt76_wcid;
> > diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> > index bbaa1365bbda..12d60d31cb51 100644
> > --- a/drivers/net/wireless/mediatek/mt76/usb.c
> > +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> > @@ -429,6 +429,45 @@ static int mt76u_get_rx_entry_len(u8 *data, u32 data_len)
> >  	return dma_len;
> >  }
> >  
> > +static struct sk_buff *
> > +mt76u_build_rx_skb(u8 *data, int len, int buf_size)
> > +{
> > +	struct sk_buff *skb;
> > +
> > +	if (SKB_WITH_OVERHEAD(buf_size) < MT_DMA_HDR_LEN + len) {
> > +		struct page *page;
> > +		int offset;
> > +
> > +		/* slow path, not enough space for data and
> > +		 * skb_shared_info
> > +		 */
> > +		skb = alloc_skb(MT_SKB_HEAD_LEN, GFP_ATOMIC);
> > +		if (!skb)
> > +			return NULL;
> > +
> > +		skb_put_data(skb, data + MT_DMA_HDR_LEN, MT_SKB_HEAD_LEN);
> 
> I looked how rx amsdu is processed in mac80211 and it is decomposed and
> copied into newly allocated individual skb's, see ieee80211_amsdu_to_8023s()
> 
> So copy L3 & L4 headers doesn't do anything good here, actually seems to
> be better to have them in frag as __ieee80211_amsdu_copy_frag() do some
> magic to avid copy.

Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
8, thx :)
In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up
copying 32B + ether_len. Anyway I think 32 is a little bit too low and we could get
better performances increasing it a little bit.
A typical use case (e.g IPv6 + TCP):

IPv6 = 40B, TCP = 32B --> so 72B..I guess 128B is a good value :)
@Felix, Johannes: what do you think?

Regarding the patch I guess let's apply it as it is in order to fix the pending
issue and then we will figure out how to proceed (copy hdr_len + 3 or increase
the value in __ieee80211_amsdu_copy)

Regards,
Lorenzo

> 
> Stanislaw

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Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Johannes Berg]

On Fri, 2019-06-14 at 12:11 +0200, Lorenzo Bianconi wrote:

> Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
> 8, thx :)
> In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up
> copying 32B + ether_len. Anyway I think 32 is a little bit too low and we could get
> better performances increasing it a little bit.
> A typical use case (e.g IPv6 + TCP):
> 
> IPv6 = 40B, TCP = 32B --> so 72B..I guess 128B is a good value :)
> @Felix, Johannes: what do you think?

I think while we might *allocate* more, I don't think we should *copy*
more, since then the TCP payload will no longer be in pages.

It'd probably be better to implement leaving enough tailroom (allocate
128), but copying nothing, unless the *entire* packet fits.

johannes

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

[Lorenzo Bianconi]

[-- Attachment #1: Type: text/plain, Size: 1937 bytes --]

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

[Stanislaw Gruszka]

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

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Stanislaw Gruszka]

On Fri, Jun 14, 2019 at 12:11:17PM +0200, Lorenzo Bianconi wrote:
> > On Thu, Jun 13, 2019 at 11:43:11PM +0200, Lorenzo Bianconi wrote:
> > > Commit f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes
> > > for rx") breaks A-MSDU support. When A-MSDU is enable the device can
> > > receive frames up to q->buf_size but they will be discarded in
> > > mt76u_process_rx_entry since there is no enough room for
> > > skb_shared_info. Fix the issue reallocating the skb and copying in the
> > > linear area the first 128B of the received frames and in the frag_list
> > > the remaining part.
> > > 
> > > Fixes: f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes for rx")
> > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > ---
> > >  drivers/net/wireless/mediatek/mt76/mt76.h |  1 +
> > >  drivers/net/wireless/mediatek/mt76/usb.c  | 49 ++++++++++++++++++-----
> > >  2 files changed, 41 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> > > index 8ecbf81a906f..889b76deb703 100644
> > > --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> > > +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> > > @@ -30,6 +30,7 @@
> > >  #define MT_TX_RING_SIZE     256
> > >  #define MT_MCU_RING_SIZE    32
> > >  #define MT_RX_BUF_SIZE      2048
> > > +#define MT_SKB_HEAD_LEN     128
> > >  
> > >  struct mt76_dev;
> > >  struct mt76_wcid;
> > > diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> > > index bbaa1365bbda..12d60d31cb51 100644
> > > --- a/drivers/net/wireless/mediatek/mt76/usb.c
> > > +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> > > @@ -429,6 +429,45 @@ static int mt76u_get_rx_entry_len(u8 *data, u32 data_len)
> > >  	return dma_len;
> > >  }
> > >  
> > > +static struct sk_buff *
> > > +mt76u_build_rx_skb(u8 *data, int len, int buf_size)
> > > +{
> > > +	struct sk_buff *skb;
> > > +
> > > +	if (SKB_WITH_OVERHEAD(buf_size) < MT_DMA_HDR_LEN + len) {
> > > +		struct page *page;
> > > +		int offset;
> > > +
> > > +		/* slow path, not enough space for data and
> > > +		 * skb_shared_info
> > > +		 */
> > > +		skb = alloc_skb(MT_SKB_HEAD_LEN, GFP_ATOMIC);
> > > +		if (!skb)
> > > +			return NULL;
> > > +
> > > +		skb_put_data(skb, data + MT_DMA_HDR_LEN, MT_SKB_HEAD_LEN);
> > 
> > I looked how rx amsdu is processed in mac80211 and it is decomposed and
> > copied into newly allocated individual skb's, see ieee80211_amsdu_to_8023s()
> > 
> > So copy L3 & L4 headers doesn't do anything good here, actually seems to
> > be better to have them in frag as __ieee80211_amsdu_copy_frag() do some
> > magic to avid copy.
> 
> Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
> 8, thx :)
> In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up

I don't think reuse_frag is true in our case since skb->head_frag is
not set when we use alloc_skb(). 

Stanislaw

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Stanislaw Gruszka]

On Fri, Jun 14, 2019 at 12:20:59PM +0200, Johannes Berg wrote:
> On Fri, 2019-06-14 at 12:11 +0200, Lorenzo Bianconi wrote:
> 
> > Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
> > 8, thx :)
> > In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up
> > copying 32B + ether_len. Anyway I think 32 is a little bit too low and we could get
> > better performances increasing it a little bit.
> > A typical use case (e.g IPv6 + TCP):
> > 
> > IPv6 = 40B, TCP = 32B --> so 72B..I guess 128B is a good value :)
> > @Felix, Johannes: what do you think?
> 
> I think while we might *allocate* more, I don't think we should *copy*
> more, since then the TCP payload will no longer be in pages.
> 
> It'd probably be better to implement leaving enough tailroom (allocate
> 128), but copying nothing, unless the *entire* packet fits.

iwl4965 put entire packet in fragment in il4965_pass_packet_to_mac80211() .
Initially I thought this is a bug, since mac80211 require header be
in the linear area, but looks like ieee80211_rx_monitor() copy header
before rest of mac80211 check it, so 4965 is fine.

Anyway I think the driver should put ieee80211 header in linear area
and iwlwifi & mt7601u implementation is somewhat optimal.

Stanislaw

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Johannes Berg]

On Fri, 2019-06-14 at 13:31 +0200, Stanislaw Gruszka wrote:
> On Fri, Jun 14, 2019 at 12:20:59PM +0200, Johannes Berg wrote:
> > On Fri, 2019-06-14 at 12:11 +0200, Lorenzo Bianconi wrote:
> > 
> > > Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
> > > 8, thx :)
> > > In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up
> > > copying 32B + ether_len. Anyway I think 32 is a little bit too low and we could get
> > > better performances increasing it a little bit.
> > > A typical use case (e.g IPv6 + TCP):
> > > 
> > > IPv6 = 40B, TCP = 32B --> so 72B..I guess 128B is a good value :)
> > > @Felix, Johannes: what do you think?
> > 
> > I think while we might *allocate* more, I don't think we should *copy*
> > more, since then the TCP payload will no longer be in pages.
> > 
> > It'd probably be better to implement leaving enough tailroom (allocate
> > 128), but copying nothing, unless the *entire* packet fits.
> 
> iwl4965 put entire packet in fragment in il4965_pass_packet_to_mac80211() .
> Initially I thought this is a bug, since mac80211 require header be
> in the linear area, but looks like ieee80211_rx_monitor() copy header
> before rest of mac80211 check it, so 4965 is fine.

Mac80211 should not assume anything about header being present or not,
just like the rest of the network stack.

> Anyway I think the driver should put ieee80211 header in linear area
> and iwlwifi & mt7601u implementation is somewhat optimal.

Yes, it's just an optimisation to do the copy-break (copy small packets
completely) or to copy the header already (since we may have better ways
to do so than skb_copy_bits if we still have a virt pointer to the page,
rather than just the page pointer).

johannes

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Lorenzo Bianconi]

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> On Fri, Jun 14, 2019 at 12:11:17PM +0200, Lorenzo Bianconi wrote:
> > > On Thu, Jun 13, 2019 at 11:43:11PM +0200, Lorenzo Bianconi wrote:
> > > > Commit f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes
> > > > for rx") breaks A-MSDU support. When A-MSDU is enable the device can
> > > > receive frames up to q->buf_size but they will be discarded in
> > > > mt76u_process_rx_entry since there is no enough room for
> > > > skb_shared_info. Fix the issue reallocating the skb and copying in the
> > > > linear area the first 128B of the received frames and in the frag_list
> > > > the remaining part.
> > > > 
> > > > Fixes: f8f527b16db5 ("mt76: usb: use EP max packet aligned buffer sizes for rx")
> > > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > > ---
> > > >  drivers/net/wireless/mediatek/mt76/mt76.h |  1 +
> > > >  drivers/net/wireless/mediatek/mt76/usb.c  | 49 ++++++++++++++++++-----
> > > >  2 files changed, 41 insertions(+), 9 deletions(-)
> > > > 
> > > > diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> > > > index 8ecbf81a906f..889b76deb703 100644
> > > > --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> > > > +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> > > > @@ -30,6 +30,7 @@
> > > >  #define MT_TX_RING_SIZE     256
> > > >  #define MT_MCU_RING_SIZE    32
> > > >  #define MT_RX_BUF_SIZE      2048
> > > > +#define MT_SKB_HEAD_LEN     128
> > > >  
> > > >  struct mt76_dev;
> > > >  struct mt76_wcid;
> > > > diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> > > > index bbaa1365bbda..12d60d31cb51 100644
> > > > --- a/drivers/net/wireless/mediatek/mt76/usb.c
> > > > +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> > > > @@ -429,6 +429,45 @@ static int mt76u_get_rx_entry_len(u8 *data, u32 data_len)
> > > >  	return dma_len;
> > > >  }
> > > >  
> > > > +static struct sk_buff *
> > > > +mt76u_build_rx_skb(u8 *data, int len, int buf_size)
> > > > +{
> > > > +	struct sk_buff *skb;
> > > > +
> > > > +	if (SKB_WITH_OVERHEAD(buf_size) < MT_DMA_HDR_LEN + len) {
> > > > +		struct page *page;
> > > > +		int offset;
> > > > +
> > > > +		/* slow path, not enough space for data and
> > > > +		 * skb_shared_info
> > > > +		 */
> > > > +		skb = alloc_skb(MT_SKB_HEAD_LEN, GFP_ATOMIC);
> > > > +		if (!skb)
> > > > +			return NULL;
> > > > +
> > > > +		skb_put_data(skb, data + MT_DMA_HDR_LEN, MT_SKB_HEAD_LEN);
> > > 
> > > I looked how rx amsdu is processed in mac80211 and it is decomposed and
> > > copied into newly allocated individual skb's, see ieee80211_amsdu_to_8023s()
> > > 
> > > So copy L3 & L4 headers doesn't do anything good here, actually seems to
> > > be better to have them in frag as __ieee80211_amsdu_copy_frag() do some
> > > magic to avid copy.
> > 
> > Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
> > 8, thx :)
> > In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up
> 
> I don't think reuse_frag is true in our case since skb->head_frag is
> not set when we use alloc_skb(). 

Oh, right. In this case it is probably better to use netdev_alloc_skb().
I will repost using the approach used in mt7601u since for the moment it will
not make any difference to copy more data.

Regards,
Lorenzo

> 
> Stanislaw

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

[Lorenzo Bianconi]

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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?

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

> 
> > > 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.

tpt differences, not sure if there are any

Regards,
Lorenzo

> 
> Stanislaw

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

[Stanislaw Gruszka]

On Fri, Jun 14, 2019 at 02:46:36PM +0200, Lorenzo Bianconi wrote:
> > > 
> > > 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?
> 
> yes, it is right (we will use two pages with data_size change). Maybe better to
> use 4 pages for each rx queue entry? (otherwise we will probably change it in
> the future)

We should not allocate more than is required. If support for bigger
rx AMSDUs will be added and announced in vht/ht capabilities to remote
stations, then increase of number of segments will be needed.

> > > > 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.
> 
> tpt differences, not sure if there are any

I would not expect any measurable difference in tpt nor in cpu usage
either way.

But I think, if some AMSDU subframe will be spited into two fragments,
data most likely will need to be linearised/copied, at some point before
passed to application, what will overcome any benefit of avoiding coping
802.11 header. Thought, I don't think this somehow will be visible in
benchmarking.

Stanislaw

Re: [PATCH v3 wireless-drivers 1/3] mt76: usb: fix rx A-MSDU support

[Lorenzo Bianconi]

>
> On Fri, Jun 14, 2019 at 12:20:59PM +0200, Johannes Berg wrote:
> > On Fri, 2019-06-14 at 12:11 +0200, Lorenzo Bianconi wrote:
> >
> > > Looking at __ieee80211_amsdu_copy() now I got why other drivers copy hdrlen +
> > > 8, thx :)
> > > In our case reuse_frag is true in __ieee80211_amsdu_copy, so we will end up
> > > copying 32B + ether_len. Anyway I think 32 is a little bit too low and we could get
> > > better performances increasing it a little bit.
> > > A typical use case (e.g IPv6 + TCP):
> > >
> > > IPv6 = 40B, TCP = 32B --> so 72B..I guess 128B is a good value :)
> > > @Felix, Johannes: what do you think?
> >
> > I think while we might *allocate* more, I don't think we should *copy*
> > more, since then the TCP payload will no longer be in pages.
> >
> > It'd probably be better to implement leaving enough tailroom (allocate
> > 128), but copying nothing, unless the *entire* packet fits.
>
> iwl4965 put entire packet in fragment in il4965_pass_packet_to_mac80211() .
> Initially I thought this is a bug, since mac80211 require header be
> in the linear area, but looks like ieee80211_rx_monitor() copy header
> before rest of mac80211 check it, so 4965 is fine.
>
> Anyway I think the driver should put ieee80211 header in linear area
> and iwlwifi & mt7601u implementation is somewhat optimal.

Actually the case is a little bit different for mt76 since we need
even mt76x02_rxwi in the linear area of the received skb.
Taking that into account the requested size to copy will be:
32 + 802.11 hdr + SNAP hdr  = ~ 70B
Moreover to pass rxwi size to usb module we need to add a field in
mt76_driver_ops (e.g rxwi_size).
I will carry out some tests and if there are no differences I will
post a single patch to wireless-drivers using 128B as default size

Regards,
Lorenzo

>
> Stanislaw

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

[Lorenzo Bianconi]

[-- Attachment #1: Type: text/plain, Size: 3093 bytes --]

> On Fri, Jun 14, 2019 at 02:46:36PM +0200, Lorenzo Bianconi wrote:
> > > > 
> > > > 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?
> > 
> > yes, it is right (we will use two pages with data_size change). Maybe better to
> > use 4 pages for each rx queue entry? (otherwise we will probably change it in
> > the future)
> 
> We should not allocate more than is required. If support for bigger
> rx AMSDUs will be added and announced in vht/ht capabilities to remote
> stations, then increase of number of segments will be needed.
> 
> > > > > 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.
> > 
> > tpt differences, not sure if there are any
> 
> I would not expect any measurable difference in tpt nor in cpu usage
> either way.
> 
> But I think, if some AMSDU subframe will be spited into two fragments,
> data most likely will need to be linearised/copied, at some point before
> passed to application, what will overcome any benefit of avoiding coping
> 802.11 header. Thought, I don't think this somehow will be visible in
> benchmarking.

Sorry for the late reply. I think so.
I will post a v4 soon.

Regards,
Lorenzo

> 
> Stanislaw

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