netdev - [PATCH net] net: gro: do not keep too many GRO packets in napi->rx

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Message-Id: <20210204213146.4192368-1-eric.dumazet@gmail.com>
Date:   Thu,  4 Feb 2021 13:31:46 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        John Sperbeck <jsperbeck@...gle.com>,
        Jian Yang <jianyang@...gle.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Alexander Lobakin <alobakin@...nk.ru>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Edward Cree <ecree@...arflare.com>
Subject: [PATCH net] net: gro: do not keep too many GRO packets in napi->rx_list

From: Eric Dumazet <edumazet@...gle.com>

Commit c80794323e82 ("net: Fix packet reordering caused by GRO and
listified RX cooperation") had the unfortunate effect of adding
latencies in common workloads.

Before the patch, GRO packets were immediately passed to
upper stacks.

After the patch, we can accumulate quite a lot of GRO
packets (depdending on NAPI budget).

My fix is counting in napi->rx_count number of segments
instead of number of logical packets.

Fixes: c80794323e82 ("net: Fix packet reordering caused by GRO and listified RX cooperation")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Bisected-by: John Sperbeck <jsperbeck@...gle.com>
Tested-by: Jian Yang <jianyang@...gle.com>
Cc: Maxim Mikityanskiy <maximmi@...lanox.com>
Cc: Alexander Lobakin <alobakin@...nk.ru>
Cc: Saeed Mahameed <saeedm@...lanox.com>
Cc: Edward Cree <ecree@...arflare.com>
---
 net/core/dev.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index a979b86dbacda9dfe31dd8b269024f7f0f5a8ef1..449b45b843d40ece7dd1e2ed6a5996ee1db9f591 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5735,10 +5735,11 @@ static void gro_normal_list(struct napi_struct *napi)
 /* Queue one GRO_NORMAL SKB up for list processing. If batch size exceeded,
  * pass the whole batch up to the stack.
  */
-static void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb)
+static void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb, int segs)
 {
 	list_add_tail(&skb->list, &napi->rx_list);
-	if (++napi->rx_count >= gro_normal_batch)
+	napi->rx_count += segs;
+	if (napi->rx_count >= gro_normal_batch)
 		gro_normal_list(napi);
 }
 
@@ -5777,7 +5778,7 @@ static int napi_gro_complete(struct napi_struct *napi, struct sk_buff *skb)
 	}
 
 out:
-	gro_normal_one(napi, skb);
+	gro_normal_one(napi, skb, NAPI_GRO_CB(skb)->count);
 	return NET_RX_SUCCESS;
 }
 
@@ -6067,7 +6068,7 @@ static gro_result_t napi_skb_finish(struct napi_struct *napi,
 {
 	switch (ret) {
 	case GRO_NORMAL:
-		gro_normal_one(napi, skb);
+		gro_normal_one(napi, skb, 1);
 		break;
 
 	case GRO_DROP:
@@ -6155,7 +6156,7 @@ static gro_result_t napi_frags_finish(struct napi_struct *napi,
 		__skb_push(skb, ETH_HLEN);
 		skb->protocol = eth_type_trans(skb, skb->dev);
 		if (ret == GRO_NORMAL)
-			gro_normal_one(napi, skb);
+			gro_normal_one(napi, skb, 1);
 		break;
 
 	case GRO_DROP:
-- 
2.30.0.365.g02bc693789-goog