[RFC] usb: gadget: ncm: Add support to configure wMaSegmentSize

[RFC] usb: gadget: ncm: Add support to configure wMaSegmentSize

[Krishna Kurapati]

Currently the NCM driver restricts wMasxSegmentSize that indicates
the datagram size coming from network layer to 1514. However the
spec doesn't have any limitation.

Add support to configure this value before configfs symlink is
created. Also since the NTB Out/In buffer sizes are fixed at 16384
bytes, limit the segment size to an upper cap of 8192 bytes so that
at least 2 packets can be aggregated.

Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
---
 drivers/usb/gadget/function/f_ncm.c | 55 +++++++++++++++++++++++++++++
 drivers/usb/gadget/function/u_ncm.h |  1 +
 2 files changed, 56 insertions(+)

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index 424bb3b666db..1969e276017f 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -118,6 +118,12 @@ static inline unsigned ncm_bitrate(struct usb_gadget *g)
 /* Delay for the transmit to wait before sending an unfilled NTB frame. */
 #define TX_TIMEOUT_NSECS	300000
 
+/*
+ * Currently the max NTB Buffer size is set to 16384. For atleast 2 packets
+ * to be aggregated, the size of datagram must at max be 8192.
+ */
+#define MAX_DATAGRAM_SIZE	8192
+
 #define FORMATS_SUPPORTED	(USB_CDC_NCM_NTB16_SUPPORTED |	\
 				 USB_CDC_NCM_NTB32_SUPPORTED)
 
@@ -1440,6 +1446,7 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 	 */
 	if (!ncm_opts->bound) {
 		mutex_lock(&ncm_opts->lock);
+		ncm_opts->net->mtu = (ncm_opts->max_segment_size - 14);
 		gether_set_gadget(ncm_opts->net, cdev->gadget);
 		status = gether_register_netdev(ncm_opts->net);
 		mutex_unlock(&ncm_opts->lock);
@@ -1484,6 +1491,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 
 	status = -ENODEV;
 
+	ecm_desc.wMaxSegmentSize = ncm_opts->max_segment_size;
+
 	/* allocate instance-specific endpoints */
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
 	if (!ep)
@@ -1586,11 +1595,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
 /* f_ncm_opts_ifname */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
 
+static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
+						char *page)
+{
+	struct f_ncm_opts *opts = to_f_ncm_opts(item);
+	u32 segment_size;
+
+	mutex_lock(&opts->lock);
+	segment_size = opts->max_segment_size;
+	mutex_unlock(&opts->lock);
+
+	return sprintf(page, "%u\n", segment_size);
+}
+
+static ssize_t ncm_opts_max_segment_size_store(struct config_item *item,
+						const char *page, size_t len)
+{
+	struct f_ncm_opts *opts = to_f_ncm_opts(item);
+	int ret;
+	u32 segment_size;
+
+	mutex_lock(&opts->lock);
+	if (opts->refcnt) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	ret = kstrtou32(page, 0, &segment_size);
+	if (ret)
+		goto out;
+
+	if (segment_size > MAX_DATAGRAM_SIZE) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	opts->max_segment_size = segment_size;
+	ret = len;
+out:
+	mutex_unlock(&opts->lock);
+	return ret;
+}
+
+CONFIGFS_ATTR(ncm_opts_, max_segment_size);
+
 static struct configfs_attribute *ncm_attrs[] = {
 	&ncm_opts_attr_dev_addr,
 	&ncm_opts_attr_host_addr,
 	&ncm_opts_attr_qmult,
 	&ncm_opts_attr_ifname,
+	&ncm_opts_attr_max_segment_size,
 	NULL,
 };
 
@@ -1633,6 +1687,7 @@ static struct usb_function_instance *ncm_alloc_inst(void)
 		kfree(opts);
 		return ERR_CAST(net);
 	}
+	opts->max_segment_size = cpu_to_le16(ETH_FRAME_LEN);
 	INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
 
 	descs[0] = &opts->ncm_os_desc;
diff --git a/drivers/usb/gadget/function/u_ncm.h b/drivers/usb/gadget/function/u_ncm.h
index 5408854d8407..fab99d997476 100644
--- a/drivers/usb/gadget/function/u_ncm.h
+++ b/drivers/usb/gadget/function/u_ncm.h
@@ -31,6 +31,7 @@ struct f_ncm_opts {
 	 */
 	struct mutex			lock;
 	int				refcnt;
+	u32				max_segment_size;
 };
 
 #endif /* U_NCM_H */
-- 
2.39.0

Re: [RFC] usb: gadget: ncm: Add support to configure wMaSegmentSize

[Maciej Żenczykowski]

This isn't a review per say - just some loose comments.

On Sun, Feb 12, 2023 at 9:57 AM Krishna Kurapati
<quic_kriskura@quicinc.com> wrote:
> Currently the NCM driver restricts wMasxSegmentSize that indicates

there's a number of spelling mistakes, here, and in the commit title

> the datagram size coming from network layer to 1514. However the
> spec doesn't have any limitation.
>
> Add support to configure this value before configfs symlink is
> created. Also since the NTB Out/In buffer sizes are fixed at 16384
> bytes, limit the segment size to an upper cap of 8192 bytes so that
> at least 2 packets can be aggregated.

I've experimented with increasing mtu to boost performance before
(have some half-baked patches/scripts somewhere).
And while it did improve point-to-point performance, it wasn't
actually useful for any real world use cases,
as internet mtu is simply never above 1500.

Note that you cannot simply receive, aggregate (lro/gro) and forward
aggregated packets without splitting them back up.

A change like this to be useful would require negotiating some sort of
gso capabilities between the two devices
(and thus extending the NCM standard).  I've been meaning to do
this... but time...

> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
> ---
>  drivers/usb/gadget/function/f_ncm.c | 55 +++++++++++++++++++++++++++++
>  drivers/usb/gadget/function/u_ncm.h |  1 +
>  2 files changed, 56 insertions(+)
>
> diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
> index 424bb3b666db..1969e276017f 100644
> --- a/drivers/usb/gadget/function/f_ncm.c
> +++ b/drivers/usb/gadget/function/f_ncm.c
> @@ -118,6 +118,12 @@ static inline unsigned ncm_bitrate(struct usb_gadget *g)
>  /* Delay for the transmit to wait before sending an unfilled NTB frame. */
>  #define TX_TIMEOUT_NSECS       300000
>
> +/*
> + * Currently the max NTB Buffer size is set to 16384. For atleast 2 packets
> + * to be aggregated, the size of datagram must at max be 8192.
> + */
> +#define MAX_DATAGRAM_SIZE      8192

From what I recall, there's a fair bit of overhead, and 8192 x2
doesn't actually fit in 16384...
That said... is it reasonable to require 2 to fit?  why? what's wrong
with 15000?

> +
>  #define FORMATS_SUPPORTED      (USB_CDC_NCM_NTB16_SUPPORTED |  \
>                                  USB_CDC_NCM_NTB32_SUPPORTED)
>
> @@ -1440,6 +1446,7 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>          */
>         if (!ncm_opts->bound) {
>                 mutex_lock(&ncm_opts->lock);
> +               ncm_opts->net->mtu = (ncm_opts->max_segment_size - 14);

this should use a constant, ETH_HLEN probably

>                 gether_set_gadget(ncm_opts->net, cdev->gadget);
>                 status = gether_register_netdev(ncm_opts->net);
>                 mutex_unlock(&ncm_opts->lock);
> @@ -1484,6 +1491,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>
>         status = -ENODEV;
>
> +       ecm_desc.wMaxSegmentSize = ncm_opts->max_segment_size;
> +

Curious... wasn't this set previously?

>         /* allocate instance-specific endpoints */
>         ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
>         if (!ep)
> @@ -1586,11 +1595,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
>  /* f_ncm_opts_ifname */
>  USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
>
> +static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
> +                                               char *page)
> +{
> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
> +       u32 segment_size;
> +
> +       mutex_lock(&opts->lock);
> +       segment_size = opts->max_segment_size;
> +       mutex_unlock(&opts->lock);
> +
> +       return sprintf(page, "%u\n", segment_size);
> +}
> +
> +static ssize_t ncm_opts_max_segment_size_store(struct config_item *item,
> +                                               const char *page, size_t len)
> +{
> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
> +       int ret;
> +       u32 segment_size;
> +
> +       mutex_lock(&opts->lock);
> +       if (opts->refcnt) {
> +               ret = -EBUSY;
> +               goto out;
> +       }
> +
> +       ret = kstrtou32(page, 0, &segment_size);
> +       if (ret)
> +               goto out;
> +
> +       if (segment_size > MAX_DATAGRAM_SIZE) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +
> +       opts->max_segment_size = segment_size;
> +       ret = len;
> +out:
> +       mutex_unlock(&opts->lock);
> +       return ret;
> +}
> +
> +CONFIGFS_ATTR(ncm_opts_, max_segment_size);
> +
>  static struct configfs_attribute *ncm_attrs[] = {
>         &ncm_opts_attr_dev_addr,
>         &ncm_opts_attr_host_addr,
>         &ncm_opts_attr_qmult,
>         &ncm_opts_attr_ifname,
> +       &ncm_opts_attr_max_segment_size,
>         NULL,
>  };
>
> @@ -1633,6 +1687,7 @@ static struct usb_function_instance *ncm_alloc_inst(void)
>                 kfree(opts);
>                 return ERR_CAST(net);
>         }
> +       opts->max_segment_size = cpu_to_le16(ETH_FRAME_LEN);
>         INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
>
>         descs[0] = &opts->ncm_os_desc;
> diff --git a/drivers/usb/gadget/function/u_ncm.h b/drivers/usb/gadget/function/u_ncm.h
> index 5408854d8407..fab99d997476 100644
> --- a/drivers/usb/gadget/function/u_ncm.h
> +++ b/drivers/usb/gadget/function/u_ncm.h
> @@ -31,6 +31,7 @@ struct f_ncm_opts {
>          */
>         struct mutex                    lock;
>         int                             refcnt;
> +       u32                             max_segment_size;
>  };
>
>  #endif /* U_NCM_H */
> --
> 2.39.0
>

Re: [RFC] usb: gadget: ncm: Add support to configure wMaSegmentSize

[Krishna Kurapati PSSNV]

On 2/14/2023 3:17 AM, Maciej Żenczykowski wrote:
> This isn't a review per say - just some loose comments.
> 
> On Sun, Feb 12, 2023 at 9:57 AM Krishna Kurapati
> <quic_kriskura@quicinc.com> wrote:
>> Currently the NCM driver restricts wMasxSegmentSize that indicates
> 
> there's a number of spelling mistakes, here, and in the commit title
> 
>> the datagram size coming from network layer to 1514. However the
>> spec doesn't have any limitation.
>>
>> Add support to configure this value before configfs symlink is
>> created. Also since the NTB Out/In buffer sizes are fixed at 16384
>> bytes, limit the segment size to an upper cap of 8192 bytes so that
>> at least 2 packets can be aggregated.
> 
Hi Maciej, Thanks for the comments:

> I've experimented with increasing mtu to boost performance before
> (have some half-baked patches/scripts somewhere).
> And while it did improve point-to-point performance, it wasn't
> actually useful for any real world use cases,
> as internet mtu is simply never above 1500.
My use case is actually a P2P connection and data is not strictly 
internet data. So I was trying to change the MTU and max segment size 
both at the same time to increase throughput.
> 
> Note that you cannot simply receive, aggregate (lro/gro) and forward
> aggregated packets without splitting them back up.
> 
> A change like this to be useful would require negotiating some sort of
> gso capabilities between the two devices
> (and thus extending the NCM standard).  I've been meaning to do
> this... but time...
> 
I have very little knowledge of GSO capabilities. Will get back and read 
up on them.
Is it something to do with splitting/aggregation of packets at Phy layer 
(segments of NTB) before giving them back to network stack ?

>> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
>> ---
>>   drivers/usb/gadget/function/f_ncm.c | 55 +++++++++++++++++++++++++++++
>>   drivers/usb/gadget/function/u_ncm.h |  1 +
>>   2 files changed, 56 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
>> index 424bb3b666db..1969e276017f 100644
>> --- a/drivers/usb/gadget/function/f_ncm.c
>> +++ b/drivers/usb/gadget/function/f_ncm.c
>> @@ -118,6 +118,12 @@ static inline unsigned ncm_bitrate(struct usb_gadget *g)
>>   /* Delay for the transmit to wait before sending an unfilled NTB frame. */
>>   #define TX_TIMEOUT_NSECS       300000
>>
>> +/*
>> + * Currently the max NTB Buffer size is set to 16384. For atleast 2 packets
>> + * to be aggregated, the size of datagram must at max be 8192.
>> + */
>> +#define MAX_DATAGRAM_SIZE      8192
> 
>  From what I recall, there's a fair bit of overhead, and 8192 x2
> doesn't actually fit in 16384...
> That said... is it reasonable to require 2 to fit?  why? what's wrong
> with 15000?
Thanks for this, I missed the header being present here. I was under the 
impression that we might need to aggregate at least 2 packets. So made 
it (fixed_out_len/2). But seems like we can even put it to 15000 as 
well. Will remove this check in configfs store func.
> 
>> +
>>   #define FORMATS_SUPPORTED      (USB_CDC_NCM_NTB16_SUPPORTED |  \
>>                                   USB_CDC_NCM_NTB32_SUPPORTED)
>>
>> @@ -1440,6 +1446,7 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>>           */
>>          if (!ncm_opts->bound) {
>>                  mutex_lock(&ncm_opts->lock);
>> +               ncm_opts->net->mtu = (ncm_opts->max_segment_size - 14);
> 
> this should use a constant, ETH_HLEN probably
Sure, will make this a constant.
> 
>>                  gether_set_gadget(ncm_opts->net, cdev->gadget);
>>                  status = gether_register_netdev(ncm_opts->net);
>>                  mutex_unlock(&ncm_opts->lock);
>> @@ -1484,6 +1491,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>>
>>          status = -ENODEV;
>>
>> +       ecm_desc.wMaxSegmentSize = ncm_opts->max_segment_size;
>> +
> 
> Curious... wasn't this set previously?

The one set above was MTU size before register net device. This here is 
to update the required segment size to ecm_descriptor before requesting 
ep's and providing descs to composite.

Regards,
Krishna,
> 
>>          /* allocate instance-specific endpoints */
>>          ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
>>          if (!ep)
>> @@ -1586,11 +1595,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
>>   /* f_ncm_opts_ifname */
>>   USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
>>
>> +static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
>> +                                               char *page)
>> +{
>> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
>> +       u32 segment_size;
>> +
>> +       mutex_lock(&opts->lock);
>> +       segment_size = opts->max_segment_size;
>> +       mutex_unlock(&opts->lock);
>> +
>> +       return sprintf(page, "%u\n", segment_size);
>> +}
>> +
>> +static ssize_t ncm_opts_max_segment_size_store(struct config_item *item,
>> +                                               const char *page, size_t len)
>> +{
>> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
>> +       int ret;
>> +       u32 segment_size;
>> +
>> +       mutex_lock(&opts->lock);
>> +       if (opts->refcnt) {
>> +               ret = -EBUSY;
>> +               goto out;
>> +       }
>> +
>> +       ret = kstrtou32(page, 0, &segment_size);
>> +       if (ret)
>> +               goto out;
>> +
>> +       if (segment_size > MAX_DATAGRAM_SIZE) {
>> +               ret = -EINVAL;
>> +               goto out;
>> +       }
>> +
>> +       opts->max_segment_size = segment_size;
>> +       ret = len;
>> +out:
>> +       mutex_unlock(&opts->lock);
>> +       return ret;
>> +}
>> +
>> +CONFIGFS_ATTR(ncm_opts_, max_segment_size);
>> +
>>   static struct configfs_attribute *ncm_attrs[] = {
>>          &ncm_opts_attr_dev_addr,
>>          &ncm_opts_attr_host_addr,
>>          &ncm_opts_attr_qmult,
>>          &ncm_opts_attr_ifname,
>> +       &ncm_opts_attr_max_segment_size,
>>          NULL,
>>   };
>>
>> @@ -1633,6 +1687,7 @@ static struct usb_function_instance *ncm_alloc_inst(void)
>>                  kfree(opts);
>>                  return ERR_CAST(net);
>>          }
>> +       opts->max_segment_size = cpu_to_le16(ETH_FRAME_LEN);
>>          INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
>>
>>          descs[0] = &opts->ncm_os_desc;
>> diff --git a/drivers/usb/gadget/function/u_ncm.h b/drivers/usb/gadget/function/u_ncm.h
>> index 5408854d8407..fab99d997476 100644
>> --- a/drivers/usb/gadget/function/u_ncm.h
>> +++ b/drivers/usb/gadget/function/u_ncm.h
>> @@ -31,6 +31,7 @@ struct f_ncm_opts {
>>           */
>>          struct mutex                    lock;
>>          int                             refcnt;
>> +       u32                             max_segment_size;
>>   };
>>
>>   #endif /* U_NCM_H */
>> --
>> 2.39.0
>>

Re: [RFC] usb: gadget: ncm: Add support to configure wMaSegmentSize

[Krishna Kurapati PSSNV]

On 2/14/2023 3:17 AM, Maciej Żenczykowski wrote:
> This isn't a review per say - just some loose comments.
> 
> On Sun, Feb 12, 2023 at 9:57 AM Krishna Kurapati
> <quic_kriskura@quicinc.com> wrote:
>> Currently the NCM driver restricts wMasxSegmentSize that indicates
> 
> there's a number of spelling mistakes, here, and in the commit title
> 
>> the datagram size coming from network layer to 1514. However the
>> spec doesn't have any limitation.
>>
>> Add support to configure this value before configfs symlink is
>> created. Also since the NTB Out/In buffer sizes are fixed at 16384
>> bytes, limit the segment size to an upper cap of 8192 bytes so that
>> at least 2 packets can be aggregated.
> 
> I've experimented with increasing mtu to boost performance before
> (have some half-baked patches/scripts somewhere).
> And while it did improve point-to-point performance, it wasn't
> actually useful for any real world use cases,
> as internet mtu is simply never above 1500.
> 
> Note that you cannot simply receive, aggregate (lro/gro) and forward
> aggregated packets without splitting them back up.
One more query on this:

Would this problem come up if the MTU and segment size are consistent as 
well ? i.e., if the datagrams present in NTB are  of size <= MTU so that 
they can be given back safely to network stack without any further 
aggregation/splitup before wrap/unwrap call at usb layer ?

Regards,
Krishna,

> 
> A change like this to be useful would require negotiating some sort of
> gso capabilities between the two devices
> (and thus extending the NCM standard).  I've been meaning to do
> this... but time...
> 
>> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
>> ---
>>   drivers/usb/gadget/function/f_ncm.c | 55 +++++++++++++++++++++++++++++
>>   drivers/usb/gadget/function/u_ncm.h |  1 +
>>   2 files changed, 56 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
>> index 424bb3b666db..1969e276017f 100644
>> --- a/drivers/usb/gadget/function/f_ncm.c
>> +++ b/drivers/usb/gadget/function/f_ncm.c
>> @@ -118,6 +118,12 @@ static inline unsigned ncm_bitrate(struct usb_gadget *g)
>>   /* Delay for the transmit to wait before sending an unfilled NTB frame. */
>>   #define TX_TIMEOUT_NSECS       300000
>>
>> +/*
>> + * Currently the max NTB Buffer size is set to 16384. For atleast 2 packets
>> + * to be aggregated, the size of datagram must at max be 8192.
>> + */
>> +#define MAX_DATAGRAM_SIZE      8192
> 
>  From what I recall, there's a fair bit of overhead, and 8192 x2
> doesn't actually fit in 16384...
> That said... is it reasonable to require 2 to fit?  why? what's wrong
> with 15000?
> 
>> +
>>   #define FORMATS_SUPPORTED      (USB_CDC_NCM_NTB16_SUPPORTED |  \
>>                                   USB_CDC_NCM_NTB32_SUPPORTED)
>>
>> @@ -1440,6 +1446,7 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>>           */
>>          if (!ncm_opts->bound) {
>>                  mutex_lock(&ncm_opts->lock);
>> +               ncm_opts->net->mtu = (ncm_opts->max_segment_size - 14);
> 
> this should use a constant, ETH_HLEN probably
> 
>>                  gether_set_gadget(ncm_opts->net, cdev->gadget);
>>                  status = gether_register_netdev(ncm_opts->net);
>>                  mutex_unlock(&ncm_opts->lock);
>> @@ -1484,6 +1491,8 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
>>
>>          status = -ENODEV;
>>
>> +       ecm_desc.wMaxSegmentSize = ncm_opts->max_segment_size;
>> +
> 
> Curious... wasn't this set previously?
> 
>>          /* allocate instance-specific endpoints */
>>          ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
>>          if (!ep)
>> @@ -1586,11 +1595,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
>>   /* f_ncm_opts_ifname */
>>   USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
>>
>> +static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
>> +                                               char *page)
>> +{
>> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
>> +       u32 segment_size;
>> +
>> +       mutex_lock(&opts->lock);
>> +       segment_size = opts->max_segment_size;
>> +       mutex_unlock(&opts->lock);
>> +
>> +       return sprintf(page, "%u\n", segment_size);
>> +}
>> +
>> +static ssize_t ncm_opts_max_segment_size_store(struct config_item *item,
>> +                                               const char *page, size_t len)
>> +{
>> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
>> +       int ret;
>> +       u32 segment_size;
>> +
>> +       mutex_lock(&opts->lock);
>> +       if (opts->refcnt) {
>> +               ret = -EBUSY;
>> +               goto out;
>> +       }
>> +
>> +       ret = kstrtou32(page, 0, &segment_size);
>> +       if (ret)
>> +               goto out;
>> +
>> +       if (segment_size > MAX_DATAGRAM_SIZE) {
>> +               ret = -EINVAL;
>> +               goto out;
>> +       }
>> +
>> +       opts->max_segment_size = segment_size;
>> +       ret = len;
>> +out:
>> +       mutex_unlock(&opts->lock);
>> +       return ret;
>> +}
>> +
>> +CONFIGFS_ATTR(ncm_opts_, max_segment_size);
>> +
>>   static struct configfs_attribute *ncm_attrs[] = {
>>          &ncm_opts_attr_dev_addr,
>>          &ncm_opts_attr_host_addr,
>>          &ncm_opts_attr_qmult,
>>          &ncm_opts_attr_ifname,
>> +       &ncm_opts_attr_max_segment_size,
>>          NULL,
>>   };
>>
>> @@ -1633,6 +1687,7 @@ static struct usb_function_instance *ncm_alloc_inst(void)
>>                  kfree(opts);
>>                  return ERR_CAST(net);
>>          }
>> +       opts->max_segment_size = cpu_to_le16(ETH_FRAME_LEN);
>>          INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
>>
>>          descs[0] = &opts->ncm_os_desc;
>> diff --git a/drivers/usb/gadget/function/u_ncm.h b/drivers/usb/gadget/function/u_ncm.h
>> index 5408854d8407..fab99d997476 100644
>> --- a/drivers/usb/gadget/function/u_ncm.h
>> +++ b/drivers/usb/gadget/function/u_ncm.h
>> @@ -31,6 +31,7 @@ struct f_ncm_opts {
>>           */
>>          struct mutex                    lock;
>>          int                             refcnt;
>> +       u32                             max_segment_size;
>>   };
>>
>>   #endif /* U_NCM_H */
>> --
>> 2.39.0
>>

Re: [RFC] usb: gadget: ncm: Add support to configure wMaSegmentSize

[Krishna Kurapati PSSNV]

On 2/14/2023 6:57 AM, Krishna Kurapati PSSNV wrote:
> 
> 
> On 2/14/2023 3:17 AM, Maciej Żenczykowski wrote:
>> This isn't a review per say - just some loose comments.
>>
>> On Sun, Feb 12, 2023 at 9:57 AM Krishna Kurapati
>> <quic_kriskura@quicinc.com> wrote:
>>> Currently the NCM driver restricts wMasxSegmentSize that indicates
>>
>> there's a number of spelling mistakes, here, and in the commit title
>>
>>> the datagram size coming from network layer to 1514. However the
>>> spec doesn't have any limitation.
>>>
>>> Add support to configure this value before configfs symlink is
>>> created. Also since the NTB Out/In buffer sizes are fixed at 16384
>>> bytes, limit the segment size to an upper cap of 8192 bytes so that
>>> at least 2 packets can be aggregated.
>>
>> I've experimented with increasing mtu to boost performance before
>> (have some half-baked patches/scripts somewhere).
>> And while it did improve point-to-point performance, it wasn't
>> actually useful for any real world use cases,
>> as internet mtu is simply never above 1500.
>>
>> Note that you cannot simply receive, aggregate (lro/gro) and forward
>> aggregated packets without splitting them back up.
> One more query on this:
> 
> Would this problem come up if the MTU and segment size are consistent as 
> well ? i.e., if the datagrams present in NTB are  of size <= MTU so that 
> they can be given back safely to network stack without any further 
> aggregation/splitup before wrap/unwrap call at usb layer ?
> 
> Regards,
> Krishna,
> 
Hi Maciej Żenczykowski,

     Any thoughts on this ?
     I believe if we modify the ncm_opts->net->mtu to the datagram 
length (excluding the header) before registering net device in bind 
call, we wouldn't need to split/aggregate obtained data before giving it 
to network layer right as they would definitely be of size <= MTU of the 
net device ? I tried it out and no issue came up in iperf test.

Thanks,
Krishna,
>>
>> A change like this to be useful would require negotiating some sort of
>> gso capabilities between the two devices
>> (and thus extending the NCM standard).  I've been meaning to do
>> this... but time...
>>
>>> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
>>> ---
>>>   drivers/usb/gadget/function/f_ncm.c | 55 +++++++++++++++++++++++++++++
>>>   drivers/usb/gadget/function/u_ncm.h |  1 +
>>>   2 files changed, 56 insertions(+)
>>>
>>> diff --git a/drivers/usb/gadget/function/f_ncm.c 
>>> b/drivers/usb/gadget/function/f_ncm.c
>>> index 424bb3b666db..1969e276017f 100644
>>> --- a/drivers/usb/gadget/function/f_ncm.c
>>> +++ b/drivers/usb/gadget/function/f_ncm.c
>>> @@ -118,6 +118,12 @@ static inline unsigned ncm_bitrate(struct 
>>> usb_gadget *g)
>>>   /* Delay for the transmit to wait before sending an unfilled NTB 
>>> frame. */
>>>   #define TX_TIMEOUT_NSECS       300000
>>>
>>> +/*
>>> + * Currently the max NTB Buffer size is set to 16384. For atleast 2 
>>> packets
>>> + * to be aggregated, the size of datagram must at max be 8192.
>>> + */
>>> +#define MAX_DATAGRAM_SIZE      8192
>>
>>  From what I recall, there's a fair bit of overhead, and 8192 x2
>> doesn't actually fit in 16384...
>> That said... is it reasonable to require 2 to fit?  why? what's wrong
>> with 15000?
>>
>>> +
>>>   #define FORMATS_SUPPORTED      (USB_CDC_NCM_NTB16_SUPPORTED |  \
>>>                                   USB_CDC_NCM_NTB32_SUPPORTED)
>>>
>>> @@ -1440,6 +1446,7 @@ static int ncm_bind(struct usb_configuration 
>>> *c, struct usb_function *f)
>>>           */
>>>          if (!ncm_opts->bound) {
>>>                  mutex_lock(&ncm_opts->lock);
>>> +               ncm_opts->net->mtu = (ncm_opts->max_segment_size - 14);
>>
>> this should use a constant, ETH_HLEN probably
>>
>>>                  gether_set_gadget(ncm_opts->net, cdev->gadget);
>>>                  status = gether_register_netdev(ncm_opts->net);
>>>                  mutex_unlock(&ncm_opts->lock);
>>> @@ -1484,6 +1491,8 @@ static int ncm_bind(struct usb_configuration 
>>> *c, struct usb_function *f)
>>>
>>>          status = -ENODEV;
>>>
>>> +       ecm_desc.wMaxSegmentSize = ncm_opts->max_segment_size;
>>> +
>>
>> Curious... wasn't this set previously?
>>
>>>          /* allocate instance-specific endpoints */
>>>          ep = usb_ep_autoconfig(cdev->gadget, &fs_ncm_in_desc);
>>>          if (!ep)
>>> @@ -1586,11 +1595,56 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(ncm);
>>>   /* f_ncm_opts_ifname */
>>>   USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(ncm);
>>>
>>> +static ssize_t ncm_opts_max_segment_size_show(struct config_item *item,
>>> +                                               char *page)
>>> +{
>>> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
>>> +       u32 segment_size;
>>> +
>>> +       mutex_lock(&opts->lock);
>>> +       segment_size = opts->max_segment_size;
>>> +       mutex_unlock(&opts->lock);
>>> +
>>> +       return sprintf(page, "%u\n", segment_size);
>>> +}
>>> +
>>> +static ssize_t ncm_opts_max_segment_size_store(struct config_item 
>>> *item,
>>> +                                               const char *page, 
>>> size_t len)
>>> +{
>>> +       struct f_ncm_opts *opts = to_f_ncm_opts(item);
>>> +       int ret;
>>> +       u32 segment_size;
>>> +
>>> +       mutex_lock(&opts->lock);
>>> +       if (opts->refcnt) {
>>> +               ret = -EBUSY;
>>> +               goto out;
>>> +       }
>>> +
>>> +       ret = kstrtou32(page, 0, &segment_size);
>>> +       if (ret)
>>> +               goto out;
>>> +
>>> +       if (segment_size > MAX_DATAGRAM_SIZE) {
>>> +               ret = -EINVAL;
>>> +               goto out;
>>> +       }
>>> +
>>> +       opts->max_segment_size = segment_size;
>>> +       ret = len;
>>> +out:
>>> +       mutex_unlock(&opts->lock);
>>> +       return ret;
>>> +}
>>> +
>>> +CONFIGFS_ATTR(ncm_opts_, max_segment_size);
>>> +
>>>   static struct configfs_attribute *ncm_attrs[] = {
>>>          &ncm_opts_attr_dev_addr,
>>>          &ncm_opts_attr_host_addr,
>>>          &ncm_opts_attr_qmult,
>>>          &ncm_opts_attr_ifname,
>>> +       &ncm_opts_attr_max_segment_size,
>>>          NULL,
>>>   };
>>>
>>> @@ -1633,6 +1687,7 @@ static struct usb_function_instance 
>>> *ncm_alloc_inst(void)
>>>                  kfree(opts);
>>>                  return ERR_CAST(net);
>>>          }
>>> +       opts->max_segment_size = cpu_to_le16(ETH_FRAME_LEN);
>>>          INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
>>>
>>>          descs[0] = &opts->ncm_os_desc;
>>> diff --git a/drivers/usb/gadget/function/u_ncm.h 
>>> b/drivers/usb/gadget/function/u_ncm.h
>>> index 5408854d8407..fab99d997476 100644
>>> --- a/drivers/usb/gadget/function/u_ncm.h
>>> +++ b/drivers/usb/gadget/function/u_ncm.h
>>> @@ -31,6 +31,7 @@ struct f_ncm_opts {
>>>           */
>>>          struct mutex                    lock;
>>>          int                             refcnt;
>>> +       u32                             max_segment_size;
>>>   };
>>>
>>>   #endif /* U_NCM_H */
>>> -- 
>>> 2.39.0
>>>