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Message-ID: <20230611014527.ezkgvtac5akrprdg@ripper>
Date: Sat, 10 Jun 2023 18:45:27 -0700
From: Bjorn Andersson <andersson@...nel.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
Andy Gross <agross@...nel.org>,
Marijn Suijten <marijn.suijten@...ainline.org>,
linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] soc: qcom: icc-bwmon: Set default thresholds
dynamically
On Sat, Jun 10, 2023 at 02:01:53PM +0200, Konrad Dybcio wrote:
> Currently we use predefined threshold values. This works, but does not
> really scale well, as they may differ between SoCs due to LPDDR generation
> and/or DDR controller setup. All of the data we need for that is already
> provided in the device tree, anyway.
>
Per your own argument, the replaced values are just initial values and
you should fairly quickly get some interrupt to start moving the
threshold up or down. I don't think your argumentation expresses
adequately why this "does not really scale well" and why your new values
happens to work better.
> Change that to:
> * 0 for low (as we've been doing up until now)
> * BW_MIN/4 for mid
> * BW_MIN for high
>
> The mid value is chosen for a "low enough" bw to nudge bwmon into
> slowing down if the bw starts too high from the bootloader.
>
As soon as we get the first interrupt, these values would be adjusted to
the bandwidth of the surrounding opp pair. So why is the /4 needed in
this initial state?
> The high value corresponds to the upper barrier which - when crossed -
> raises an interrupt in the third zone, signaling a need for upping
> the bw.
>
> This only changes the values programmed at probe time, as high and med
> thresholds are updated at interrupt, based on the OPP table from DT.
>
Your underlying reasoning, to remove the hard coded initial values,
sounds very reasonable to me.
Regards,
Bjorn
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
> drivers/soc/qcom/icc-bwmon.c | 28 +++++++---------------------
> 1 file changed, 7 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/soc/qcom/icc-bwmon.c b/drivers/soc/qcom/icc-bwmon.c
> index 40068a285913..99cbdb3cf531 100644
> --- a/drivers/soc/qcom/icc-bwmon.c
> +++ b/drivers/soc/qcom/icc-bwmon.c
> @@ -165,9 +165,6 @@ enum bwmon_fields {
> struct icc_bwmon_data {
> unsigned int sample_ms;
> unsigned int count_unit_kb; /* kbytes */
> - unsigned int default_highbw_kbps;
> - unsigned int default_medbw_kbps;
> - unsigned int default_lowbw_kbps;
> u8 zone1_thres_count;
> u8 zone3_thres_count;
> unsigned int quirks;
> @@ -564,20 +561,21 @@ static void bwmon_set_threshold(struct icc_bwmon *bwmon,
> static void bwmon_start(struct icc_bwmon *bwmon)
> {
> const struct icc_bwmon_data *data = bwmon->data;
> + u32 bw_low = 0;
> int window;
>
> + /* No need to check for errors, as this must have succeeded before. */
> + dev_pm_opp_find_bw_ceil(bwmon->dev, &bw_low, 0);
> +
> bwmon_clear_counters(bwmon, true);
>
> window = mult_frac(bwmon->data->sample_ms, HW_TIMER_HZ, MSEC_PER_SEC);
> /* Maximum sampling window: 0xffffff for v4 and 0xfffff for v5 */
> regmap_field_write(bwmon->regs[F_SAMPLE_WINDOW], window);
>
> - bwmon_set_threshold(bwmon, bwmon->regs[F_THRESHOLD_HIGH],
> - data->default_highbw_kbps);
> - bwmon_set_threshold(bwmon, bwmon->regs[F_THRESHOLD_MED],
> - data->default_medbw_kbps);
> - bwmon_set_threshold(bwmon, bwmon->regs[F_THRESHOLD_LOW],
> - data->default_lowbw_kbps);
> + bwmon_set_threshold(bwmon, bwmon->regs[F_THRESHOLD_HIGH], bw_low);
> + bwmon_set_threshold(bwmon, bwmon->regs[F_THRESHOLD_MED], div_u64(bw_low, 4));
> + bwmon_set_threshold(bwmon, bwmon->regs[F_THRESHOLD_LOW], 0);
>
> regmap_field_write(bwmon->regs[F_THRESHOLD_COUNT_ZONE0],
> BWMON_THRESHOLD_COUNT_ZONE0_DEFAULT);
> @@ -807,9 +805,6 @@ static int bwmon_remove(struct platform_device *pdev)
> static const struct icc_bwmon_data msm8998_bwmon_data = {
> .sample_ms = 4,
> .count_unit_kb = 1024,
> - .default_highbw_kbps = 4800 * 1024, /* 4.8 GBps */
> - .default_medbw_kbps = 512 * 1024, /* 512 MBps */
> - .default_lowbw_kbps = 0,
> .zone1_thres_count = 16,
> .zone3_thres_count = 1,
> .quirks = BWMON_HAS_GLOBAL_IRQ,
> @@ -822,9 +817,6 @@ static const struct icc_bwmon_data msm8998_bwmon_data = {
> static const struct icc_bwmon_data sdm845_cpu_bwmon_data = {
> .sample_ms = 4,
> .count_unit_kb = 64,
> - .default_highbw_kbps = 4800 * 1024, /* 4.8 GBps */
> - .default_medbw_kbps = 512 * 1024, /* 512 MBps */
> - .default_lowbw_kbps = 0,
> .zone1_thres_count = 16,
> .zone3_thres_count = 1,
> .quirks = BWMON_HAS_GLOBAL_IRQ,
> @@ -835,9 +827,6 @@ static const struct icc_bwmon_data sdm845_cpu_bwmon_data = {
> static const struct icc_bwmon_data sdm845_llcc_bwmon_data = {
> .sample_ms = 4,
> .count_unit_kb = 1024,
> - .default_highbw_kbps = 800 * 1024, /* 800 MBps */
> - .default_medbw_kbps = 256 * 1024, /* 256 MBps */
> - .default_lowbw_kbps = 0,
> .zone1_thres_count = 16,
> .zone3_thres_count = 1,
> .regmap_fields = sdm845_llcc_bwmon_reg_fields,
> @@ -847,9 +836,6 @@ static const struct icc_bwmon_data sdm845_llcc_bwmon_data = {
> static const struct icc_bwmon_data sc7280_llcc_bwmon_data = {
> .sample_ms = 4,
> .count_unit_kb = 64,
> - .default_highbw_kbps = 800 * 1024, /* 800 MBps */
> - .default_medbw_kbps = 256 * 1024, /* 256 MBps */
> - .default_lowbw_kbps = 0,
> .zone1_thres_count = 16,
> .zone3_thres_count = 1,
> .quirks = BWMON_NEEDS_FORCE_CLEAR,
>
> ---
> base-commit: 49dd846128d56199db2e3bcfca42d87fbc82b212
> change-id: 20230610-topic-bwmon_opp-f995bbdd18bd
>
> Best regards,
> --
> Konrad Dybcio <konrad.dybcio@...aro.org>
>
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