Re: [PATCH 03/20] common/cnxk: adjust shaper rates to lower boundaries

[Nithin Kumar Dabilpuram <ndabilpuram@marvell.com>]

Please see inline.

On 2/17/22 6:50 PM, Jerin Jacob wrote:
> On Mon, Feb 7, 2022 at 1:00 PM Nithin Dabilpuram
> <ndabilpuram@marvell.com> wrote:
>>
>> From: Satha Rao <skoteshwar@marvell.com>
>>
>> New api to get floor values for a requested shaper rate, which can assure
> 
> Since it is internal API, no need to mention in the comment log
> 
>> packets should never be transmitted at a rate higher than configured.
>>
>> Keep the old api to get HW suggested values.
>> And introduce new parameter to select appropriate api.
> 
> api -> API
> 
>>
>> Signed-off-by: Satha Rao <skoteshwar@marvell.com>
>> ---
>> +static uint64_t
>> +nix_tm_shaper_rate_conv_floor(uint64_t value, uint64_t *exponent_p,
>> +                             uint64_t *mantissa_p, uint64_t *div_exp_p)
>> +{
>> +       uint64_t div_exp, exponent, mantissa;
>> +
>> +       /* Boundary checks */
>> +       if (value < NIX_TM_MIN_SHAPER_RATE || value > NIX_TM_MAX_SHAPER_RATE)
>> +               return 0;
>> +
>> +       if (value <= NIX_TM_SHAPER_RATE(0, 0, 0)) {
>> +               /* Calculate rate div_exp and mantissa using
>> +                * the following formula:
>> +                *
>> +                * value = (2E6 * (256 + mantissa)
>> +                *              / ((1 << div_exp) * 256))
>> +                */
>> +               div_exp = 0;
>> +               exponent = 0;
>> +               mantissa = NIX_TM_MAX_RATE_MANTISSA;
>> +
>> +               while (value <= (NIX_TM_SHAPER_RATE_CONST / (1 << div_exp)))
>> +                       div_exp += 1;
>> +
>> +               while (value <= ((NIX_TM_SHAPER_RATE_CONST * (256 + mantissa)) /
>> +                                ((1 << div_exp) * 256)))
>> +                       mantissa -= 1;
> 
> Please move this as another static function.
This is not same as the non-floor function though it looks same. The 
while loops terminate in <= in this function. Do you still need sub 
functions for these ?
> 
> 
>> +       } else {
>> +               /* Calculate rate exponent and mantissa using
>> +                * the following formula:
>> +                *
>> +                * value = (2E6 * ((256 + mantissa) << exponent)) / 256
>> +                *
>> +                */
>> +               div_exp = 0;
>> +               exponent = NIX_TM_MAX_RATE_EXPONENT;
>> +               mantissa = NIX_TM_MAX_RATE_MANTISSA;
>> +
>> +               while (value <= (NIX_TM_SHAPER_RATE_CONST * (1 << exponent)))
>> +                       exponent -= 1;
>> +
>> +               while (value <= ((NIX_TM_SHAPER_RATE_CONST *
>> +                                 ((256 + mantissa) << exponent)) /
>> +                                256))
>> +                       mantissa -= 1;
> 
> Please move this as another static function.
Same comment as above.
> 
>> +       }
>> +
>> +       if (div_exp > NIX_TM_MAX_RATE_DIV_EXP ||
>> +           exponent > NIX_TM_MAX_RATE_EXPONENT ||
>> +           mantissa > NIX_TM_MAX_RATE_MANTISSA)
>> +               return 0;
>> +
>> +       if (div_exp_p)
>> +               *div_exp_p = div_exp;
>> +       if (exponent_p)
>> +               *exponent_p = exponent;
>> +       if (mantissa_p)
>> +               *mantissa_p = mantissa;
>> +
>> +       /* Calculate real rate value */
>> +       return NIX_TM_SHAPER_RATE(exponent, mantissa, div_exp);
>> +}
>> +
>> +static uint64_t
>> +nix_tm_shaper_rate_conv_exact(uint64_t value, uint64_t *exponent_p,
>> +                             uint64_t *mantissa_p, uint64_t *div_exp_p)
>>   {
>>          uint64_t div_exp, exponent, mantissa;
>>
>> @@ -188,6 +251,23 @@ nix_tm_shaper_rate_conv(uint64_t value, uint64_t *exponent_p,
>>          return NIX_TM_SHAPER_RATE(exponent, mantissa, div_exp);
>>   }
>>
>> +/* With zero accuracy we will tune parameters as defined by HW,
>> + * non zero accuracy will keep the parameters close to lower values
>> + * and make sure long term shaper rate will not exceed requested rate.
> 
> long-term
> requested -> the requested