linux-kernel - cpu performance drop between 4.18 and 5.10 kernel?

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Date: Wed, 22 May 2024 07:44:34 +0000
From: mengkanglai <mengkanglai2@...wei.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>, Simon Horman
	<horms@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, "Sebastian
 Andrzej Siewior" <bigeasy@...utronix.de>, Lorenzo Bianconi
	<lorenzo@...nel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, open
 list <linux-kernel@...r.kernel.org>
CC: "Fengtao (fengtao, Euler)" <fengtao40@...wei.com>, "Yanan (Euler)"
	<yanan@...wei.com>
Subject: cpu performance drop between 4.18 and 5.10 kernel?

Dear maintainers:
I updated my VM kernel from 4.18 to 5.10, and found that the CPU SI usage was higher under the 5.10 kernel for the same udp service.
I captured the flame graph and compared the two versions of kernels. 
Kernel 5.10 compared to 4.18 napi_complete_done function added gro_normal_list call (ommit 323ebb61e32b4 ("net: use listified RX for handling GRO_NORMAL
skbs") Introduced), I removed gro_normal_list from napi_complete_done in 5.10 kernel, CPU SI usages was same as 4.18.
I don't know much about GRO, so I'm not sure if it can be modified in this way, and the consequences of such a modification?