[PATCH] net/mlx5: fix Committed Bucket Size calculation

[PATCH] net/mlx5: fix Committed Bucket Size calculation

[Alexander Kozyrev]

Committed Bucket Size calculation tries to fit into 8-bit wide
mantissa field by setting 256 as a maximum value for it.
To compensate for this increase in the mantissa value the exponent
value has to be reduced by 8. But it gives a negative exponent
value for CBS less than 128. And negative exponent value is not
supported by the NIC. Adjust CSB calculation only for values
bigger than 128 to allow both small and big bucket sizes.

Fixes: 3bd26b23cef ("net/mlx5: support meter profile operations")
Cc: stable@dpdk.org

Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
---
 drivers/net/mlx5/mlx5_flow_meter.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_flow_meter.c b/drivers/net/mlx5/mlx5_flow_meter.c
index 0dc7fbfb32..d0f8bcd100 100644
--- a/drivers/net/mlx5/mlx5_flow_meter.c
+++ b/drivers/net/mlx5/mlx5_flow_meter.c
@@ -295,8 +295,10 @@ mlx5_flow_meter_xbs_man_exp_calc(uint64_t xbs, uint8_t *man, uint8_t *exp)
 	}
 	/* xbs = xbs_mantissa * 2^xbs_exponent */
 	_man = frexp(xbs, &_exp);
-	_man = _man * pow(2, MLX5_MAN_WIDTH);
-	_exp = _exp - MLX5_MAN_WIDTH;
+	if (_exp >= MLX5_MAN_WIDTH) {
+		_man = _man * pow(2, MLX5_MAN_WIDTH);
+		_exp = _exp - MLX5_MAN_WIDTH;
+	}
 	*man = (uint8_t)ceil(_man);
 	*exp = _exp;
 }
-- 
2.18.2

RE: [PATCH] net/mlx5: fix Committed Bucket Size calculation

[Raslan Darawsheh]

Hi,

> -----Original Message-----
> From: Alexander Kozyrev <akozyrev@nvidia.com>
> Sent: Monday, February 7, 2022 3:29 PM
> To: dev@dpdk.org
> Cc: stable@dpdk.org; Raslan Darawsheh <rasland@nvidia.com>; Slava
> Ovsiienko <viacheslavo@nvidia.com>; Matan Azrad <matan@nvidia.com>;
> Suanming Mou <suanmingm@nvidia.com>
> Subject: [PATCH] net/mlx5: fix Committed Bucket Size calculation
> 
> Committed Bucket Size calculation tries to fit into 8-bit wide
> mantissa field by setting 256 as a maximum value for it.
> To compensate for this increase in the mantissa value the exponent
> value has to be reduced by 8. But it gives a negative exponent
> value for CBS less than 128. And negative exponent value is not
> supported by the NIC. Adjust CSB calculation only for values
> bigger than 128 to allow both small and big bucket sizes.
> 
> Fixes: 3bd26b23cef ("net/mlx5: support meter profile operations")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
> Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>

Patch applied to next-net-mlx,

Kindest regards,
Raslan Darawsheh