[dpdk-dev] [PATCH] compress/mlx5: fix level translation in xform API

[Raja Zidane <rzidane@nvidia.com>]

Compression Level is interpreted by each PMD differently.
However, lower numbers give faster compression
at the expense of compression ratio, while higher numbers
may give better compression ratios but are likely slower.
The level affects the block size, which affects performance,
the bigger the block, the faster the compression is.

The problem was that higher levels caused bigger blocks:
  size = min_block_size - 1 + level.

the solution is to reverse the above:
  size = max_block_size + 1 - level.

Fixes: 39a2c8715f8f ("compress/mlx5: add transformation operations")
Cc: matan@nvidia.com
Cc: stable@dpdk.org

Signed-off-by: Raja Zidane <rzidane@nvidia.com>
---
 drivers/compress/mlx5/mlx5_compress.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/compress/mlx5/mlx5_compress.c b/drivers/compress/mlx5/mlx5_compress.c
index 5c2b9dc859..883e720ec1 100644
--- a/drivers/compress/mlx5/mlx5_compress.c
+++ b/drivers/compress/mlx5/mlx5_compress.c
@@ -316,12 +316,19 @@ mlx5_compress_xform_create(struct rte_compressdev *dev,
 			size /= MLX5_GGA_COMP_WIN_SIZE_UNITS;
 			xfrm->gga_ctrl1 += RTE_MIN(rte_log2_u32(size),
 					 MLX5_COMP_MAX_WIN_SIZE_CONF) <<
-					   WQE_GGA_COMP_WIN_SIZE_OFFSET;
-			if (xform->compress.level == RTE_COMP_LEVEL_PMD_DEFAULT)
+						WQE_GGA_COMP_WIN_SIZE_OFFSET;
+			switch (xform->compress.level) {
+			case RTE_COMP_LEVEL_PMD_DEFAULT:
 				size = MLX5_GGA_COMP_LOG_BLOCK_SIZE_MAX;
-			else
-				size = priv->min_block_size - 1 +
-							  xform->compress.level;
+				break;
+			case RTE_COMP_LEVEL_MAX:
+				size = priv->min_block_size;
+				break;
+			default:
+				size = RTE_MAX(MLX5_GGA_COMP_LOG_BLOCK_SIZE_MAX
+					+ 1 - xform->compress.level,
+					priv->min_block_size);
+			}
 			xfrm->gga_ctrl1 += RTE_MIN(size,
 					    MLX5_GGA_COMP_LOG_BLOCK_SIZE_MAX) <<
 						 WQE_GGA_COMP_BLOCK_SIZE_OFFSET;
-- 
2.27.0