IPSec tunnel throughput performance degrades

dastathagata

I am using x86 based platform where I have compared throughput performance through IPSec tunnel in two Linux kernel version. One is 4.9.337 and another is 5.10.209. In 4.9.337, I am getting TCP bidirectional throughput as 620 Mbps whereas in 5.10.209 I am getting 410 Mbps. I have observed that ipgre_xmit() is taking more CPU in 5.10.209 compared to 4.9.337. On further debugging, I have noticed that different encryption algorithm is used in those two versions of Linux kernel. In 4.9.337, _encrypt_by_4_encrypt is used whereas in 5.10.209, _crypt_by_4_78 is used.

Is it a known issue that IPSec tunnel performance degrades in 5.10.209 version compared to 4.9.337?
Is there any way to improve the throughput?