linux-kernel - Re: [RFC PATCH 2/5] scsi: ufs: Add UFS-feature layer

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Date:   Fri, 12 Jun 2020 11:27:59 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Bart Van Assche <bvanassche@....org>,
        Daejun Park <daejun7.park@...sung.com>,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        "avri.altman@....com" <avri.altman@....com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>
Subject: Re: [RFC PATCH 2/5] scsi: ufs: Add UFS-feature layer

Hi Bart,

On 2020-06-04 18:30, Daejun Park wrote:
> > +inline void ufsf_slave_configure(struct ufs_hba *hba,
> > +         struct scsi_device *sdev)
> > +{
> > +  /* skip well-known LU */
> > +  if (sdev->lun >= UFS_UPIU_MAX_UNIT_NUM_ID)
> > +    return;
> > +
> > +  if (!(hba->dev_info.b_ufs_feature_sup & UFS_FEATURE_SUPPORT_HPB_BIT))
> > +    return;
> > +
> > +  atomic_inc(&hba->ufsf.slave_conf_cnt);
> > +  smp_mb__after_atomic(); /* for slave_conf_cnt */
> > +
> > +  /* waiting sdev init.*/
> > +  if (waitqueue_active(&hba->ufsf.sdev_wait))
> > +    wake_up(&hba->ufsf.sdev_wait);
> > +}

> Guarding a wake_up() call with a waitqueue_active() check is an
> anti-pattern. Please don't do that and call wake_up() directly.
> Additionally, wake_up() includes a barrier if it wakes up a kernel
> thread so the smp_mb__after_atomic() can be left out if the
> waitqueue_active() call is removed.
OK, I will change it.

> > +/**
> > + * struct ufsf_operation - UFS feature specific callbacks
> > + * @prep_fn: called after construct upiu structure
> > + * @reset: called after proving hba
                           ^^^^^^^
> Is this a typo? Should "proving" perhaps be changed into "probing"?
Yes, I will change.

> > +struct ufshpb_driver {
> > +  struct device_driver drv;
> > +  struct list_head lh_hpb_lu;
> > +
> > +  struct ufsf_operation ufshpb_ops;
> > +
> > +  /* memory management */
> > +  struct kmem_cache *ufshpb_mctx_cache;
> > +  mempool_t *ufshpb_mctx_pool;
> > +  mempool_t *ufshpb_page_pool;
> > +
> > +  struct workqueue_struct *ufshpb_wq;
> > +};

> Why is a dedicated workqueue needed? Why are the standard workqueues not
> good enough?
The map_work handles map related operations, including IO operations. So, adding
this task to the standard WQ can interfere with other jobs and degrade HPB related performance.


> > @@ -2525,6 +2525,8 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
> >  
> >    ufshcd_comp_scsi_upiu(hba, lrbp);
> >  
> > +  ufsf_ops_prep_fn(hba, lrbp);
> > +
> >    err = ufshcd_map_sg(hba, lrbp);
> >    if (err) {
> >      lrbp->cmd = NULL;

> What happens if a SCSI command is retried and hence ufsf_ops_prep_fn()
> is called multiple times for the same SCSI command?
Developers of UFS features should implement it so that prep_fn does not have
any problems even if it processes the same SCSI command multiple times.
In HPB feature, prep_fn modifies only upiu  structure. So it is ok to call
it multiple times because the upiu is rebuilt from ufshcd_comp_scsi_upiu().

Thanks,

Daejun.