netdev - [PATCH net-next v2] net: save some cycles when doing skb_attempt_defer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20240412030718.68016-1-kerneljasonxing@gmail.com>
Date: Fri, 12 Apr 2024 11:07:18 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: edumazet@...gle.com,
	pablo@...filter.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	davem@...emloft.net,
	horms@...nel.org,
	aleksander.lobakin@...el.com
Cc: netdev@...r.kernel.org,
	kerneljasonxing@...il.com,
	Jason Xing <kernelxing@...cent.com>
Subject: [PATCH net-next v2] net: save some cycles when doing skb_attempt_defer_free()

From: Jason Xing <kernelxing@...cent.com>

Normally, we don't face these two exceptions very often meanwhile
we have some chance to meet the condition where the current cpu id
is the same as skb->alloc_cpu.

One simple test that can help us see the frequency of this statement
'cpu == raw_smp_processor_id()':
1. running iperf -s and iperf -c [ip] -P [MAX CPU]
2. using BPF to capture skb_attempt_defer_free()

I can see around 4% chance that happens to satisfy the statement.
So moving this statement at the beginning can save some cycles in
most cases.

Signed-off-by: Jason Xing <kernelxing@...cent.com>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>
---
v2
Link: https://lore.kernel.org/all/20240411032450.51649-1-kerneljasonxing@gmail.com/
1. Fix the wrong order of testing cpu (Eric)
---
 net/core/skbuff.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ab970ded8a7b..6dc577a3ea6a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -7002,9 +7002,9 @@ void skb_attempt_defer_free(struct sk_buff *skb)
 	unsigned int defer_max;
 	bool kick;
 
-	if (WARN_ON_ONCE(cpu >= nr_cpu_ids) ||
-	    !cpu_online(cpu) ||
-	    cpu == raw_smp_processor_id()) {
+	if (cpu == raw_smp_processor_id() ||
+	    WARN_ON_ONCE(cpu >= nr_cpu_ids) ||
+	    !cpu_online(cpu)) {
 nodefer:	kfree_skb_napi_cache(skb);
 		return;
 	}
-- 
2.37.3