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CONFIG_CRYPTO_DEV_QCE_SW_MAX_LEN: Default maximum request size to use software for AES

General informations

The Linux kernel configuration item CONFIG_CRYPTO_DEV_QCE_SW_MAX_LEN:

Help text

This sets the default maximum request size to perform AES requests using software instead of the crypto engine. It can be changed by setting the aes_sw_max_len parameter.

Small blocks are processed faster in software than hardware. Considering the 256-bit ciphers, software is 2-3 times faster than qce at 256-bytes, 30% faster at 512, and about even at 768-bytes. With 128-bit keys, the break-even point would be around 1024-bytes.

The default is set a little lower, to 512 bytes, to balance the cost in CPU usage. The minimum recommended setting is 16-bytes (1 AES block), since AES-GCM will fail if you set it lower. Setting this to zero will send all requests to the hardware.

Note that 192-bit keys are not supported by the hardware and are always processed by the software fallback, and all DES requests are done by the hardware.



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