diff mbox series

mac80211: mesh: add mesh_param "mesh_nolearn" to skip path discovery

Message ID 20200616095358.20143-1-linus.luessing@c0d3.blue
State Not Applicable, archived
Delegated to: Simon Wunderlich
Headers show
Series mac80211: mesh: add mesh_param "mesh_nolearn" to skip path discovery | expand

Commit Message

Linus Lüssing June 16, 2020, 9:53 a.m. UTC
From: Linus Lüssing <ll@simonwunderlich.de>

Currently, before being able to forward a packet between two 802.11s
nodes, both a PLINK handshake is performed upon receiving a beacon and
then later a PREQ/PREP exchange for path discovery is performed on
demand upon receiving a data frame to forward.

When running a mesh protocol on top of an 802.11s interface, like
batman-adv, we do not need the multi-hop mesh routing capabilities of
802.11s and usually set mesh_fwding=0. However, even with mesh_fwding=0
the PREQ/PREP path discovery is still performed on demand. Even though
in this scenario the next hop PREQ/PREP will determine is always the
direct 11s neighbor node.

The new mesh_nolearn parameter allows to skip the PREQ/PREP exchange in
this scenario, leading to a reduced delay, reduced packet buffering and
simplifies HWMP in general.

mesh_nolearn is still rather conservative in that if the packet destination
is not a direct 11s neighbor, it will fall back to PREQ/PREP path
discovery.

For normal, multi-hop 802.11s mesh routing it is usually not advisable
to enable mesh_nolearn as a transmission to a direct but distant neighbor
might be worse than reaching that same node via a more robust /
higher throughput etc. multi-hop path.

Cc: Sven Eckelmann <sven@narfation.org>
Cc: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Linus Lüssing <ll@simonwunderlich.de>
---
 include/net/cfg80211.h        |  6 ++++++
 include/uapi/linux/nl80211.h  |  7 +++++++
 net/mac80211/cfg.c            |  2 ++
 net/mac80211/debugfs_netdev.c |  2 ++
 net/mac80211/mesh_hwmp.c      | 39 +++++++++++++++++++++++++++++++++++
 net/wireless/mesh.c           |  1 +
 net/wireless/nl80211.c        |  8 ++++++-
 net/wireless/trace.h          |  4 +++-
 8 files changed, 67 insertions(+), 2 deletions(-)

Comments

Linus Lüssing June 16, 2020, 10:16 a.m. UTC | #1
> The new mesh_nolearn parameter allows to skip the PREQ/PREP exchange in
> this scenario, leading to a reduced delay, reduced packet buffering and
> simplifies HWMP in general.

Also another small remark regarding the simplification:

Next to the timer re-arming bug / crash [0] we also stumbled over 
another bug when using encryption on the 802.11s interfaces which we 
could quite solve yet:

We are seeing packet loss every four seconds due to a "DECRYPT CRC ERR". 
We could narrow this down to the PREQ. This somehow makes the receiver 
unable to decrypt the packet in hardware and also the fallback to 
software decryption fails as the hardware has messed up the encrypted 
data (looks completely different than what we saw in the air with a 
third device in monitor mode, unencrypted headers looked ok though). 
Furthermore, the hardware still sends ACKs for this frame... so no 
retries on the 802.11 layer, leading to ugly packet loss for one UDP 
packet every four seconds.

The hardware we were having this issue with is a Lima board with a QCA4531.

Setting ath9k nohwcrypt=1 on the sender side helps. And avoiding PREQs 
with this patch also helped in our batman-adv setup which had 
mesh_fwding disabled already anyway.

Regards, Linus


PS/Disclaimer: This bug was observed on an old LEDE version.


[0]: https://patchwork.kernel.org/patch/11566011/
Linus Lüssing June 17, 2020, 7:45 a.m. UTC | #2
On 16/06/2020 12:16, Linus Lüssing wrote:
>> The new mesh_nolearn parameter allows to skip the PREQ/PREP exchange in
>> this scenario, leading to a reduced delay, reduced packet buffering and
>> simplifies HWMP in general.

And a third observation we've made with HWMP:

When running iperf with 16 parallel TCP streams and the default HWMP 
parameters over two 4x4 802.11ac Wave 2 wifi cards transmitting about 
800-1000 MBit/s in total, HWMP becomes quite unstable. We see frequent 
PREQ/PREP retransmissions and also PERR messages, leading to spurious 
break downs in the throughput.

When using just 8 TCP streams, so with a little less saturation and 
stress of the channel, iperf staticstics are stable.


So maybe there would be some potential for optimizations, too, like 
somehow prioritizing HWMP messages more, or maybe making the default 
HWMP parameters a bit more conservative.


Or just disabling the HWMP PREP/PREQ/PERR exchange with this new 
configuration option would at least help the ones that are using another 
mesh routing protocol on top, who are maybe more familiar with the 
parameters of their specific routing protocol than with the HWMP parameters.

Regards, Linus
diff mbox series

Patch

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index fc7e8807838d..5ffb35592a23 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -1853,6 +1853,11 @@  struct bss_parameters {
  *      connected to a mesh gate in mesh formation info.  If false, the
  *      value in mesh formation is determined by the presence of root paths
  *      in the mesh path table
+ * @dot11MeshNolearn: Try to avoid multi-hop path discovery (e.g. PREQ/PREP
+ *      for HWMP) if the destination is a direct neighbor. Note that this might
+ *      not be the optimal decision as a multi-hop route might be better. So
+ *      if using this setting you will likely also want to disable
+ *      dot11MeshForwarding and use another mesh routing protocol on top.
  */
 struct mesh_config {
 	u16 dot11MeshRetryTimeout;
@@ -1884,6 +1889,7 @@  struct mesh_config {
 	enum nl80211_mesh_power_mode power_mode;
 	u16 dot11MeshAwakeWindowDuration;
 	u32 plink_timeout;
+	bool dot11MeshNolearn;
 };
 
 /**
diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index 4e6339ab1fce..f6560bb9644c 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -4236,6 +4236,12 @@  enum nl80211_mesh_power_mode {
  *	field.  If left unset then the mesh formation field will only
  *	advertise such if there is an active root mesh path.
  *
+ * @NL80211_MESHCONF_NOLEARN: Try to avoid multi-hop path discovery (e.g.
+ *      PREQ/PREP for HWMP) if the destination is a direct neighbor. Note that
+ *      this might not be the optimal decision as a multi-hop route might be
+ *      better. So if using this setting you will likely also want to disable
+ *      dot11MeshForwarding and use another mesh routing protocol on top.
+ *
  * @__NL80211_MESHCONF_ATTR_AFTER_LAST: internal use
  */
 enum nl80211_meshconf_params {
@@ -4269,6 +4275,7 @@  enum nl80211_meshconf_params {
 	NL80211_MESHCONF_AWAKE_WINDOW,
 	NL80211_MESHCONF_PLINK_TIMEOUT,
 	NL80211_MESHCONF_CONNECTED_TO_GATE,
+	NL80211_MESHCONF_NOLEARN,
 
 	/* keep last */
 	__NL80211_MESHCONF_ATTR_AFTER_LAST,
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 9b360544ad6f..f48e095e912a 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -2126,6 +2126,8 @@  static int ieee80211_update_mesh_config(struct wiphy *wiphy,
 	if (_chg_mesh_attr(NL80211_MESHCONF_CONNECTED_TO_GATE, mask))
 		conf->dot11MeshConnectedToMeshGate =
 			nconf->dot11MeshConnectedToMeshGate;
+	if (_chg_mesh_attr(NL80211_MESHCONF_NOLEARN, mask))
+		conf->dot11MeshNolearn = nconf->dot11MeshNolearn;
 	ieee80211_mbss_info_change_notify(sdata, BSS_CHANGED_BEACON);
 	return 0;
 }
diff --git a/net/mac80211/debugfs_netdev.c b/net/mac80211/debugfs_netdev.c
index d7e955127d5c..09eab2c3f380 100644
--- a/net/mac80211/debugfs_netdev.c
+++ b/net/mac80211/debugfs_netdev.c
@@ -638,6 +638,7 @@  IEEE80211_IF_FILE(dot11MeshAwakeWindowDuration,
 		  u.mesh.mshcfg.dot11MeshAwakeWindowDuration, DEC);
 IEEE80211_IF_FILE(dot11MeshConnectedToMeshGate,
 		  u.mesh.mshcfg.dot11MeshConnectedToMeshGate, DEC);
+IEEE80211_IF_FILE(dot11MeshNolearn, u.mesh.mshcfg.dot11MeshNolearn, DEC);
 #endif
 
 #define DEBUGFS_ADD_MODE(name, mode) \
@@ -762,6 +763,7 @@  static void add_mesh_config(struct ieee80211_sub_if_data *sdata)
 	MESHPARAMS_ADD(power_mode);
 	MESHPARAMS_ADD(dot11MeshAwakeWindowDuration);
 	MESHPARAMS_ADD(dot11MeshConnectedToMeshGate);
+	MESHPARAMS_ADD(dot11MeshNolearn);
 #undef MESHPARAMS_ADD
 }
 #endif
diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index aa5150929996..cbf94c0b408f 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -1117,6 +1117,40 @@  void mesh_path_start_discovery(struct ieee80211_sub_if_data *sdata)
 	kfree(preq_node);
 }
 
+/**
+ * mesh_nexthop_resolve_nolearn - try to set next hop without path discovery
+ * @skb: 802.11 frame to be sent
+ * @sdata: network subif the frame will be sent through
+ *
+ * Check if the meshDA (addr3) of a unicast frame is a direct neighbor.
+ * And if so, set the RA (addr1) to it to transmit to this node directly,
+ * avoiding PREP/PREP path discovery.
+ *
+ * Returns: 0 if the next hop was found and -ENOENT otherwise.
+ */
+static int mesh_nexthop_resolve_nolearn(struct ieee80211_sub_if_data *sdata,
+					struct sk_buff *skb)
+{
+	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
+	struct sta_info *sta;
+
+	if (is_multicast_ether_addr(hdr->addr1))
+		return -ENOENT;
+
+	rcu_read_lock();
+	sta = sta_info_get(sdata, hdr->addr3);
+
+	if (!sta || sta->mesh->plink_state != NL80211_PLINK_ESTAB) {
+		rcu_read_unlock();
+		return -ENOENT;
+	}
+	rcu_read_unlock();
+
+	memcpy(hdr->addr1, hdr->addr3, ETH_ALEN);
+	memcpy(hdr->addr2, sdata->vif.addr, ETH_ALEN);
+	return 0;
+}
+
 /**
  * mesh_nexthop_resolve - lookup next hop; conditionally start path discovery
  *
@@ -1132,6 +1166,7 @@  void mesh_path_start_discovery(struct ieee80211_sub_if_data *sdata)
 int mesh_nexthop_resolve(struct ieee80211_sub_if_data *sdata,
 			 struct sk_buff *skb)
 {
+	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 	struct mesh_path *mpath;
@@ -1146,6 +1181,10 @@  int mesh_nexthop_resolve(struct ieee80211_sub_if_data *sdata,
 	if (info->control.flags & IEEE80211_TX_CTRL_SKIP_MPATH_LOOKUP)
 		return 0;
 
+	if (ifmsh->mshcfg.dot11MeshNolearn &&
+	    !mesh_nexthop_resolve_nolearn(sdata, skb))
+		return 0;
+
 	if (!mesh_nexthop_lookup(sdata, skb))
 		return 0;
 
diff --git a/net/wireless/mesh.c b/net/wireless/mesh.c
index eac5aa1419fc..e4e363138279 100644
--- a/net/wireless/mesh.c
+++ b/net/wireless/mesh.c
@@ -78,6 +78,7 @@  const struct mesh_config default_mesh_config = {
 	.power_mode = NL80211_MESH_POWER_ACTIVE,
 	.dot11MeshAwakeWindowDuration = MESH_DEFAULT_AWAKE_WINDOW,
 	.plink_timeout = MESH_DEFAULT_PLINK_TIMEOUT,
+	.dot11MeshNolearn = false,
 };
 
 const struct mesh_setup default_mesh_setup = {
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 263ae395ad44..b0b7f110064f 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -6884,7 +6884,9 @@  static int nl80211_get_mesh_config(struct sk_buff *skb,
 	    nla_put_u32(msg, NL80211_MESHCONF_PLINK_TIMEOUT,
 			cur_params.plink_timeout) ||
 	    nla_put_u8(msg, NL80211_MESHCONF_CONNECTED_TO_GATE,
-		       cur_params.dot11MeshConnectedToMeshGate))
+		       cur_params.dot11MeshConnectedToMeshGate) ||
+	    nla_put_u8(msg, NL80211_MESHCONF_NOLEARN,
+		       cur_params.dot11MeshNolearn))
 		goto nla_put_failure;
 	nla_nest_end(msg, pinfoattr);
 	genlmsg_end(msg, hdr);
@@ -6942,6 +6944,7 @@  nl80211_meshconf_params_policy[NL80211_MESHCONF_ATTR_MAX+1] = {
 	[NL80211_MESHCONF_AWAKE_WINDOW] = { .type = NLA_U16 },
 	[NL80211_MESHCONF_PLINK_TIMEOUT] = { .type = NLA_U32 },
 	[NL80211_MESHCONF_CONNECTED_TO_GATE] = NLA_POLICY_RANGE(NLA_U8, 0, 1),
+	[NL80211_MESHCONF_NOLEARN] = { .type = NLA_U8 },
 };
 
 static const struct nla_policy
@@ -7093,6 +7096,9 @@  do {									\
 				  NL80211_MESHCONF_AWAKE_WINDOW, nla_get_u16);
 	FILL_IN_MESH_PARAM_IF_SET(tb, cfg, plink_timeout, mask,
 				  NL80211_MESHCONF_PLINK_TIMEOUT, nla_get_u32);
+	FILL_IN_MESH_PARAM_IF_SET(tb, cfg, dot11MeshNolearn, 0, 1,
+				  mask, NL80211_MESHCONF_NOLEARN,
+				  nl80211_check_bool);
 	if (mask_out)
 		*mask_out = mask;
 
diff --git a/net/wireless/trace.h b/net/wireless/trace.h
index b23cab016521..6e218a0acd4e 100644
--- a/net/wireless/trace.h
+++ b/net/wireless/trace.h
@@ -68,7 +68,8 @@ 
 		       __field(u16, ht_opmode)				   \
 		       __field(u32, dot11MeshHWMPactivePathToRootTimeout)  \
 		       __field(u16, dot11MeshHWMProotInterval)		   \
-		       __field(u16, dot11MeshHWMPconfirmationInterval)
+		       __field(u16, dot11MeshHWMPconfirmationInterval)	   \
+		       __field(bool, dot11MeshNolearn)
 #define MESH_CFG_ASSIGN							      \
 	do {								      \
 		__entry->dot11MeshRetryTimeout = conf->dot11MeshRetryTimeout; \
@@ -109,6 +110,7 @@ 
 				conf->dot11MeshHWMProotInterval;	      \
 		__entry->dot11MeshHWMPconfirmationInterval =		      \
 				conf->dot11MeshHWMPconfirmationInterval;      \
+		__entry->dot11MeshNolearn = conf->dot11MeshNolearn;	      \
 	} while (0)
 
 #define CHAN_ENTRY __field(enum nl80211_band, band) \