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Date:   Tue, 03 Aug 2021 15:01:42 +0200
From:   Antoine Tenart <>
To:     Sebastian Rehms <>,
Subject: Re: MACSec performance issues

Hello Sebastian,

Quoting Sebastian Rehms (2021-08-03 13:48:59)
> We did some performance tests on MACSec and observed data rates of about
> 5-6 GBits/s. (measured with iperf3)
> After a kernel update the maximum data rate dropped to about 600 MBit/s.
> Due to this huge difference we did some further investigations and found
> that the main reason is a change in the file drivers/net/macsec.c in the
> function crypto_alloc_aead().
> The change was introduced by commit
> 0899ff04c872463455f2749d13a5d311338021a3 (upstream commit
> ab046a5d4be4c90a3952a0eae75617b49c0cb01b)
> -       tfm = crypto_alloc_aead("gcm(aes)", 0, 0);
> +       /* Pick a sync gcm(aes) cipher to ensure order is preserved. */
> +       tfm = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
> According to the commit description, the  CRYPTO_ALG_ASYNC flag is
> required to guarantee correct packet ordering which is indeed an
> implicit provision of the MACSec standard.
> First, it would be desirable to verify, that the impact of the flag is
> large not only on our hardware but that it is a general phenomenon.

FYI, performance issues with CRYPTO_ALG_ASYNC was reported and discussed
in the following thread:


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