linux-kernel - RE: [PATCH v3] scsi: ufs: wb: Add explicit flush

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Date:   Fri, 9 Jun 2023 07:35:54 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     Lu Hongfei <luhongfei@...o.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Bart Van Assche <bvanassche@....org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jinyoung Choi <j-young.choi@...sung.com>,
        Daniil Lunev <dlunev@...omium.org>,
        Peter Wang <peter.wang@...iatek.com>,
        "open list:UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER" 
        <linux-scsi@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
CC:     "opensource.kernel@...o.com" <opensource.kernel@...o.com>
Subject: RE: [PATCH v3] scsi: ufs: wb: Add explicit flush_threshold sysfs
 attribute

> 
> There are three flags that control Write Booster Feature:
> 
>     1. WB ON/OFF
>     2. WB Hibern Flush ON/OFF (implicitly)
>     3. WB Flush ON/OFF (explicit)
> 
> In the case of "Hibern Flush", one of the conditions for flush WB buffer is that
> avail_wb_buff < wb_flush_threshold.
> 
> As we know, different users have different requirements for power
> consumption and performance. Therefore, we need the ability to manually
> set wb_flush_threshold, so that users can easily and flexibly adjust the
> wb_flush_threshold value, thereby achieving a balance between power
> consumption and performance.
> 
> So the sysfs attribute that controls this is necessary.
> 
> The meaning of wb_flush_threshold is the percentage of WB's total size, such
> as 1 representing 10%, 2 representing 20%, and so on.
> 
> Signed-off-by: Lu Hongfei <luhongfei@...o.com>
> ---
> The modifications made compared to the previous version are as follows:
> 1. Using 'wb_flush_threshold == 0' insted of 'wb_flush_threshold <= 0'.
> 
>  drivers/ufs/core/ufs-sysfs.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)

You are missing sysfs documentation.
> 
> diff --git a/drivers/ufs/core/ufs-sysfs.c b/drivers/ufs/core/ufs-sysfs.c index
> cdf3d5f2b77b..347207f4e8ee
> --- a/drivers/ufs/core/ufs-sysfs.c
> +++ b/drivers/ufs/core/ufs-sysfs.c
> @@ -298,6 +298,37 @@ static ssize_t enable_wb_buf_flush_store(struct
> device *dev,
>         return res < 0 ? res : count;
>  }
> 
> +static ssize_t wb_flush_threshold_show(struct device *dev,
> +                                        struct device_attribute *attr,
> +                                        char *buf) {
> +       struct ufs_hba *hba = dev_get_drvdata(dev);
> +
> +       return sysfs_emit(buf, "%u\n", hba->vps->wb_flush_threshold); }
> +
> +static ssize_t wb_flush_threshold_store(struct device *dev,
> +                                         struct device_attribute *attr,
> +                                         const char *buf, size_t count)
> +{
> +       struct ufs_hba *hba = dev_get_drvdata(dev);
> +       unsigned int wb_flush_threshold;
> +
> +       if (kstrtouint(buf, 0, &wb_flush_threshold))
> +               return -EINVAL;
Maybe also make note if wb not supported:
if (!ufshcd_is_wb_allowed(hba)  {
               dev_info(dev, "It is not allowed to configure WB buf flushing!\n");
               return -EOPNOTSUPP;
       }

Thanks,
Avri
> +
> +       /* The range of values for wb_flush_threshold is (0,10] */
> +       if (wb_flush_threshold > UFS_WB_BUF_REMAIN_PERCENT(100) ||
> +               wb_flush_threshold == 0) {
> +               dev_err(dev, "The value of wb_flush_threshold is invalid!\n");
> +               return -EINVAL;
> +       }
> +
> +       hba->vps->wb_flush_threshold = wb_flush_threshold;
> +
> +       return count;
> +}
> +
>  static DEVICE_ATTR_RW(rpm_lvl);
>  static DEVICE_ATTR_RO(rpm_target_dev_state);
>  static DEVICE_ATTR_RO(rpm_target_link_state);
> @@ -307,6 +338,7 @@ static DEVICE_ATTR_RO(spm_target_link_state);
>  static DEVICE_ATTR_RW(auto_hibern8);
>  static DEVICE_ATTR_RW(wb_on);
>  static DEVICE_ATTR_RW(enable_wb_buf_flush);
> +static DEVICE_ATTR_RW(wb_flush_threshold);
> 
>  static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
>         &dev_attr_rpm_lvl.attr,
> @@ -318,6 +350,7 @@ static struct attribute *ufs_sysfs_ufshcd_attrs[] = {
>         &dev_attr_auto_hibern8.attr,
>         &dev_attr_wb_on.attr,
>         &dev_attr_enable_wb_buf_flush.attr,
> +       &dev_attr_wb_flush_threshold.attr,
>         NULL
>  };
> 
> --
> 2.39.0