Re: [PATCH] crypto: qat - lower priority for skcipher and aead algorithms

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Jun 13, 2025 at 11:32:27AM +0100, Giovanni Cabiddu wrote:
> Most kernel applications utilizing the crypto API operate synchronously
> and on small buffer sizes, therefore do not benefit from QAT acceleration.
> 
> Reduce the priority of QAT implementations for both skcipher and aead
> algorithms, allowing more suitable alternatives to be selected by default.
> 
> Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Link: https://lore.kernel.org/all/20250613012357.GA3603104@google.com/
> Cc: stable@vger.kernel.org
> ---
>  drivers/crypto/intel/qat/qat_common/qat_algs.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/crypto/intel/qat/qat_common/qat_algs.c b/drivers/crypto/intel/qat/qat_common/qat_algs.c
> index 3c4bba4a8779..d69cc1e5e023 100644
> --- a/drivers/crypto/intel/qat/qat_common/qat_algs.c
> +++ b/drivers/crypto/intel/qat/qat_common/qat_algs.c
> @@ -1277,7 +1277,7 @@ static struct aead_alg qat_aeads[] = { {
>  	.base = {
>  		.cra_name = "authenc(hmac(sha1),cbc(aes))",
>  		.cra_driver_name = "qat_aes_cbc_hmac_sha1",
> -		.cra_priority = 4001,
> +		.cra_priority = 100,
>  		.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY,
>  		.cra_blocksize = AES_BLOCK_SIZE,
>  		.cra_ctxsize = sizeof(struct qat_alg_aead_ctx),
> @@ -1294,7 +1294,7 @@ static struct aead_alg qat_aeads[] = { {
>  	.base = {
>  		.cra_name = "authenc(hmac(sha256),cbc(aes))",
>  		.cra_driver_name = "qat_aes_cbc_hmac_sha256",
> -		.cra_priority = 4001,
> +		.cra_priority = 100,
>  		.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY,
>  		.cra_blocksize = AES_BLOCK_SIZE,
>  		.cra_ctxsize = sizeof(struct qat_alg_aead_ctx),
> @@ -1311,7 +1311,7 @@ static struct aead_alg qat_aeads[] = { {
>  	.base = {
>  		.cra_name = "authenc(hmac(sha512),cbc(aes))",
>  		.cra_driver_name = "qat_aes_cbc_hmac_sha512",
> -		.cra_priority = 4001,
> +		.cra_priority = 100,
>  		.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY,
>  		.cra_blocksize = AES_BLOCK_SIZE,
>  		.cra_ctxsize = sizeof(struct qat_alg_aead_ctx),
> @@ -1329,7 +1329,7 @@ static struct aead_alg qat_aeads[] = { {
>  static struct skcipher_alg qat_skciphers[] = { {
>  	.base.cra_name = "cbc(aes)",
>  	.base.cra_driver_name = "qat_aes_cbc",
> -	.base.cra_priority = 4001,
> +	.base.cra_priority = 100,
>  	.base.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY,
>  	.base.cra_blocksize = AES_BLOCK_SIZE,
>  	.base.cra_ctxsize = sizeof(struct qat_alg_skcipher_ctx),
> @@ -1347,7 +1347,7 @@ static struct skcipher_alg qat_skciphers[] = { {
>  }, {
>  	.base.cra_name = "ctr(aes)",
>  	.base.cra_driver_name = "qat_aes_ctr",
> -	.base.cra_priority = 4001,
> +	.base.cra_priority = 100,
>  	.base.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_ALLOCATES_MEMORY,
>  	.base.cra_blocksize = 1,
>  	.base.cra_ctxsize = sizeof(struct qat_alg_skcipher_ctx),
> @@ -1365,7 +1365,7 @@ static struct skcipher_alg qat_skciphers[] = { {
>  }, {
>  	.base.cra_name = "xts(aes)",
>  	.base.cra_driver_name = "qat_aes_xts",
> -	.base.cra_priority = 4001,
> +	.base.cra_priority = 100,
>  	.base.cra_flags = CRYPTO_ALG_ASYNC | CRYPTO_ALG_NEED_FALLBACK |
>  			  CRYPTO_ALG_ALLOCATES_MEMORY,
>  	.base.cra_blocksize = AES_BLOCK_SIZE,
> -- 
> 2.49.0
> 

Acked-by: Eric Biggers <ebiggers@kernel.org>

But, I think your commit message may be misleading:

> Most kernel applications utilizing the crypto API operate synchronously
> and on small buffer sizes, therefore do not benefit from QAT acceleration.

That implies that QAT acceleration *would* be beneficial for kernel applications
using asynchronous processing, large buffer sizes, or both.

But as far as I know, that hasn't been shown to be true either.  Those things
would likely make the performance characteristics of the QAT driver less bad,
but that doesn't necessarily mean it would become better than VAES.  VAES is
already incredibly fast, and far easier to use.

- Eric