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Date:   Mon, 22 Apr 2019 19:45:37 +0200
From:   Florian Westphal <>
To:     Vakul Garg <>
Cc:     "" <>
Subject: Re: ipsec tunnel performance degrade

Vakul Garg <> wrote:
> Post kernel 4.9, I am experiencing more than 50% degrade in ipsec performance on my arm64 based systems (with onchip crypto accelerator).
> (We use only lts kernels). My understanding is that it is mainly due to xfrm flow cache removal in version 4.12.

Yes, likely.

> I am not sure whether any subsequent work could recover the lost performance.
> With kernel 4.19, I see that xfrm_state_find() is taking a lot of cpu (more than 15%).

Can you share details about the setup?

I.e., how many policies, states etc.?
Do you use xfrm interfaces?

> Further, perf show that a lot of atomic primitives such as __ll_sc___cmpxchg_case_mb_4(), 
> __ll_sc_atomic_sub_return() are being invoked. On 16 core system, they consume more than 30% of cpu.

Thats not good, perhaps we should look at pcpu refcounts for the xfrm
state structs.

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