[openwrt/openwrt] kernel: backport GRO improvements

Sun Sep 6 09:36:27 EDT 2020

nbd pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/ba72ed537c4a063e1143b9efae579112fee7c42a

commit ba72ed537c4a063e1143b9efae579112fee7c42a
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Sun Sep 6 13:29:48 2020 +0200

    kernel: backport GRO improvements
    
    Improves network performance
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 ...low-fast-GRO-for-skbs-with-Ethernet-heade.patch | 78 ++++++++++++++++++++++
 ...e-listified-Rx-for-GRO_NORMAL-in-napi_gro.patch | 51 ++++++++++++++
 ...80-NET-skip-GRO-for-foreign-MAC-addresses.patch |  2 +-
 3 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/target/linux/generic/backport-5.4/700-v5.5-net-core-allow-fast-GRO-for-skbs-with-Ethernet-heade.patch b/target/linux/generic/backport-5.4/700-v5.5-net-core-allow-fast-GRO-for-skbs-with-Ethernet-heade.patch
new file mode 100644
index 0000000000..f864a7899c
--- /dev/null
+++ b/target/linux/generic/backport-5.4/700-v5.5-net-core-allow-fast-GRO-for-skbs-with-Ethernet-heade.patch
@@ -0,0 +1,78 @@
+From: Alexander Lobakin <alobakin at dlink.ru>
+Date: Fri, 15 Nov 2019 12:11:35 +0300
+Subject: [PATCH] net: core: allow fast GRO for skbs with Ethernet header in
+ head
+
+Commit 78d3fd0b7de8 ("gro: Only use skb_gro_header for completely
+non-linear packets") back in May'09 (v2.6.31-rc1) has changed the
+original condition '!skb_headlen(skb)' to
+'skb->mac_header == skb->tail' in gro_reset_offset() saying: "Since
+the drivers that need this optimisation all provide completely
+non-linear packets" (note that this condition has become the current
+'skb_mac_header(skb) == skb_tail_pointer(skb)' later with commmit
+ced14f6804a9 ("net: Correct comparisons and calculations using
+skb->tail and skb-transport_header") without any functional changes).
+
+For now, we have the following rough statistics for v5.4-rc7:
+1) napi_gro_frags: 14
+2) napi_gro_receive with skb->head containing (most of) payload: 83
+3) napi_gro_receive with skb->head containing all the headers: 20
+4) napi_gro_receive with skb->head containing only Ethernet header: 2
+
+With the current condition, fast GRO with the usage of
+NAPI_GRO_CB(skb)->frag0 is available only in the [1] case.
+Packets pushed by [2] and [3] go through the 'slow' path, but
+it's not a problem for them as they already contain all the needed
+headers in skb->head, so pskb_may_pull() only moves skb->data.
+
+The layout of skbs in the fourth [4] case at the moment of
+dev_gro_receive() is identical to skbs that have come through [1],
+as napi_frags_skb() pulls Ethernet header to skb->head. The only
+difference is that the mentioned condition is always false for them,
+because skb_put() and friends irreversibly alter the tail pointer.
+They also go through the 'slow' path, but now every single
+pskb_may_pull() in every single .gro_receive() will call the *really*
+slow __pskb_pull_tail() to pull headers to head. This significantly
+decreases the overall performance for no visible reasons.
+
+The only two users of method [4] is:
+* drivers/staging/qlge
+* drivers/net/wireless/iwlwifi (all three variants: dvm, mvm, mvm-mq)
+
+Note that in case with wireless drivers we can't use [1]
+(napi_gro_frags()) at least for now and mac80211 stack always
+performs pushes and pulls anyways, so performance hit is inavoidable.
+
+At the moment of v2.6.31 the mentioned change was necessary (that's
+why I don't add the "Fixes:" tag), but it became obsolete since
+skb_gro_mac_header() has gone in commit a50e233c50db ("net-gro:
+restore frag0 optimization"), so we can simply revert the condition
+in gro_reset_offset() to allow skbs from [4] go through the 'fast'
+path just like in case [1].
+
+This was tested on a 600 MHz MIPS CPU and a custom driver and this
+patch gave boosts up to 40 Mbps to method [4] in both directions
+comparing to net-next, which made overall performance relatively
+close to [1] (without it, [4] is the slowest).
+
+v2:
+- Add more references and explanations to commit message
+- Fix some typos ibid
+- No functional changes
+
+Signed-off-by: Alexander Lobakin <alobakin at dlink.ru>
+Signed-off-by: David S. Miller <davem at davemloft.net>
+---
+
+--- a/net/core/dev.c
++++ b/net/core/dev.c
+@@ -5403,8 +5403,7 @@ static void skb_gro_reset_offset(struct
+ 	NAPI_GRO_CB(skb)->frag0 = NULL;
+ 	NAPI_GRO_CB(skb)->frag0_len = 0;
+ 
+-	if (skb_mac_header(skb) == skb_tail_pointer(skb) &&
+-	    pinfo->nr_frags &&
++	if (!skb_headlen(skb) && pinfo->nr_frags &&
+ 	    !PageHighMem(skb_frag_page(frag0))) {
+ 		NAPI_GRO_CB(skb)->frag0 = skb_frag_address(frag0);
+ 		NAPI_GRO_CB(skb)->frag0_len = min_t(unsigned int,
diff --git a/target/linux/generic/backport-5.4/701-v5.5-net-core-use-listified-Rx-for-GRO_NORMAL-in-napi_gro.patch b/target/linux/generic/backport-5.4/701-v5.5-net-core-use-listified-Rx-for-GRO_NORMAL-in-napi_gro.patch
new file mode 100644
index 0000000000..7be25f5338
--- /dev/null
+++ b/target/linux/generic/backport-5.4/701-v5.5-net-core-use-listified-Rx-for-GRO_NORMAL-in-napi_gro.patch
@@ -0,0 +1,51 @@
+From: Alexander Lobakin <alobakin at dlink.ru>
+Date: Mon, 14 Oct 2019 11:00:33 +0300
+Subject: [PATCH] net: core: use listified Rx for GRO_NORMAL in
+ napi_gro_receive()
+
+Commit 323ebb61e32b4 ("net: use listified RX for handling GRO_NORMAL
+skbs") made use of listified skb processing for the users of
+napi_gro_frags().
+The same technique can be used in a way more common napi_gro_receive()
+to speed up non-merged (GRO_NORMAL) skbs for a wide range of drivers
+including gro_cells and mac80211 users.
+This slightly changes the return value in cases where skb is being
+dropped by the core stack, but it seems to have no impact on related
+drivers' functionality.
+gro_normal_batch is left untouched as it's very individual for every
+single system configuration and might be tuned in manual order to
+achieve an optimal performance.
+
+Signed-off-by: Alexander Lobakin <alobakin at dlink.ru>
+Acked-by: Edward Cree <ecree at solarflare.com>
+Signed-off-by: David S. Miller <davem at davemloft.net>
+---
+
+--- a/net/core/dev.c
++++ b/net/core/dev.c
+@@ -5601,12 +5601,13 @@ static void napi_skb_free_stolen_head(st
+ 	kmem_cache_free(skbuff_head_cache, skb);
+ }
+ 
+-static gro_result_t napi_skb_finish(gro_result_t ret, struct sk_buff *skb)
++static gro_result_t napi_skb_finish(struct napi_struct *napi,
++				    struct sk_buff *skb,
++				    gro_result_t ret)
+ {
+ 	switch (ret) {
+ 	case GRO_NORMAL:
+-		if (netif_receive_skb_internal(skb))
+-			ret = GRO_DROP;
++		gro_normal_one(napi, skb);
+ 		break;
+ 
+ 	case GRO_DROP:
+@@ -5638,7 +5639,7 @@ gro_result_t napi_gro_receive(struct nap
+ 
+ 	skb_gro_reset_offset(skb);
+ 
+-	ret = napi_skb_finish(dev_gro_receive(napi, skb), skb);
++	ret = napi_skb_finish(napi, skb, dev_gro_receive(napi, skb));
+ 	trace_napi_gro_receive_exit(ret);
+ 
+ 	return ret;
diff --git a/target/linux/generic/pending-5.4/680-NET-skip-GRO-for-foreign-MAC-addresses.patch b/target/linux/generic/pending-5.4/680-NET-skip-GRO-for-foreign-MAC-addresses.patch
index 5acadeceb1..5ba7f3e693 100644
--- a/target/linux/generic/pending-5.4/680-NET-skip-GRO-for-foreign-MAC-addresses.patch
+++ b/target/linux/generic/pending-5.4/680-NET-skip-GRO-for-foreign-MAC-addresses.patch
@@ -32,7 +32,7 @@ Signed-off-by: Felix Fietkau <nbd at nbd.name>
  	__u16			tc_index;	/* traffic control index */
 --- a/net/core/dev.c
 +++ b/net/core/dev.c
-@@ -5469,6 +5469,9 @@ static enum gro_result dev_gro_receive(s
+@@ -5468,6 +5468,9 @@ static enum gro_result dev_gro_receive(s
  	int same_flow;
  	int grow;
  

