summaryrefslogtreecommitdiffstats
path: root/net/core
diff options
context:
space:
mode:
authorAlexander Lobakin <alobakin@dlink.ru>2019-11-15 12:11:35 +0300
committerDavid S. Miller <davem@davemloft.net>2019-11-16 12:59:50 -0800
commit8aef998df3979faa19626acf889abecb733342db (patch)
tree486d212bd5da9625c4db4a7882c3df3eed6721b3 /net/core
parentf92e88dbd46147fa34a3151acce0959d8b221e06 (diff)
downloadlinux-8aef998df3979faa19626acf889abecb733342db.tar.bz2
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@dlink.ru> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core')
-rw-r--r--net/core/dev.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index 1c799d486623..da78a433c10c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5611,8 +5611,7 @@ static void skb_gro_reset_offset(struct sk_buff *skb)
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,