From ffe4ccd359d006eba559cb1a3c6113144b7fb38c Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 7 Jan 2026 10:41:59 +0000 Subject: net: add net.core.qdisc_max_burst In blamed commit, I added a check against the temporary queue built in __dev_xmit_skb(). Idea was to drop packets early, before any spinlock was acquired. if (unlikely(defer_count > READ_ONCE(q->limit))) { kfree_skb_reason(skb, SKB_DROP_REASON_QDISC_DROP); return NET_XMIT_DROP; } It turned out that HTB Qdisc has a zero q->limit. HTB limits packets on a per-class basis. Some of our tests became flaky. Add a new sysctl : net.core.qdisc_max_burst to control how many packets can be stored in the temporary lockless queue. Also add a new QDISC_BURST_DROP drop reason to better diagnose future issues. Thanks Neal ! Fixes: 100dfa74cad9 ("net: dev_queue_xmit() llist adoption") Reported-and-bisected-by: Neal Cardwell Signed-off-by: Eric Dumazet Reviewed-by: Neal Cardwell Link: https://patch.msgid.link/20260107104159.3669285-1-edumazet@google.com Signed-off-by: Paolo Abeni --- Documentation/admin-guide/sysctl/net.rst | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'Documentation/admin-guide/sysctl') diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst index 369a738a6819..91fa4ccd326c 100644 --- a/Documentation/admin-guide/sysctl/net.rst +++ b/Documentation/admin-guide/sysctl/net.rst @@ -303,6 +303,14 @@ netdev_max_backlog Maximum number of packets, queued on the INPUT side, when the interface receives packets faster than kernel can process them. +qdisc_max_burst +------------------ + +Maximum number of packets that can be temporarily stored before +reaching qdisc. + +Default: 1000 + netdev_rss_key -------------- -- cgit v1.2.3