linux-kernel - Re: [PATCH v2 04/10] interconnect: qcom: icc-rpm: Check for node-specific rate coefficients

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Date:   Tue, 1 Aug 2023 13:01:50 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v2 04/10] interconnect: qcom: icc-rpm: Check for
 node-specific rate coefficients

On Mon, Jul 31, 2023 at 12:52:20PM +0200, Konrad Dybcio wrote:
> Some nodes may have different coefficients than the general values for
> bus they're attached to. Check for that and use them if present.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>  drivers/interconnect/qcom/icc-rpm.c | 10 +++++++---
>  drivers/interconnect/qcom/icc-rpm.h |  6 ++++++
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/interconnect/qcom/icc-rpm.c b/drivers/interconnect/qcom/icc-rpm.c
> index f0e575c95b49..91eb428385f6 100644
> --- a/drivers/interconnect/qcom/icc-rpm.c
> +++ b/drivers/interconnect/qcom/icc-rpm.c
> @@ -300,11 +300,15 @@ static u64 qcom_icc_calc_rate(struct qcom_icc_provider *qp, struct qcom_icc_node
>  	else
>  		agg_avg_rate = qn->sum_avg[ctx];
>  
> -	/* Check if the node has a specific coefficient first*/
> -	if (qp->ab_coeff)
> +	/* Check if the node has a specific coefficient first */
> +	if (qn->ab_coeff)
> +		agg_avg_rate = mult_frac(qn->ab_coeff, agg_avg_rate, 100);
> +	else if (qp->ab_coeff)
>  		agg_avg_rate = mult_frac(qp->ab_coeff, agg_avg_rate, 100);
>  
> -	if (qp->ib_coeff)
> +	if (qn->ab_coeff)
> +		agg_peak_rate = mult_frac(100, qn->max_peak[ctx], qn->ib_coeff);
> +	else if (qp->ib_coeff)
>  		agg_peak_rate = mult_frac(100, qn->max_peak[ctx], qp->ib_coeff);
>  	else
>  		agg_peak_rate = qn->max_peak[ctx];

Code/data size and likely performance would be slightly better if you
only add ab_coeff/ib_coeff to the node and not the provider. This is
slightly inconvenient because you need to duplicate the same value on
a lot of nodes, but the per-node memory is reserved anyway. You might
as well use I would say.

> diff --git a/drivers/interconnect/qcom/icc-rpm.h b/drivers/interconnect/qcom/icc-rpm.h
> index 835b83cfb548..1a26a7b82166 100644
> --- a/drivers/interconnect/qcom/icc-rpm.h
> +++ b/drivers/interconnect/qcom/icc-rpm.h
> @@ -103,6 +103,9 @@ struct qcom_icc_qos {
>   * @mas_rpm_id:	RPM id for devices that are bus masters
>   * @slv_rpm_id:	RPM id for devices that are bus slaves
>   * @qos: NoC QoS setting parameters
> + * @ab_coeff: a percentage-based coefficient for compensating the AB calculations
> + * @ib_coeff: an inverse-percentage-based coefficient for compensating the IB calculations
> + * @bus_clk_rate: a pointer to an array containing bus clock rates in Hz
>   */
>  struct qcom_icc_node {
>  	unsigned char *name;
> @@ -117,6 +120,9 @@ struct qcom_icc_node {
>  	int mas_rpm_id;
>  	int slv_rpm_id;
>  	struct qcom_icc_qos qos;
> +	u16 ab_coeff;
> +	u16 ib_coeff;
> +	u32 *bus_clk_rate;

bus_clk_rate should be in previous patch :)

Thanks,
Stephan