Commit 4d0470b9 authored by Jason Xing's avatar Jason Xing Committed by David S. Miller
Browse files

net: save some cycles when doing skb_attempt_defer_free() 



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: default avatarJason Xing <kernelxing@tencent.com>
Reviewed-by: default avatarAlexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 71329c49

net/core/skbuff.c

+3 −3
Original line number Diff line number Diff line
@@ -6965,9 +6965,9 @@ 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;

	}