Re: [PATCH v29 4/4] scsi: ufs: Add HPB 2.0 support

[Can Guo]

On 2021-03-17 09:42, Daejun Park wrote:
> > On 2021-03-15 15:23, Can Guo wrote:
> > > On 2021-03-15 15:07, Daejun Park wrote:
> > > > > > This patch supports the HPB 2.0.
> > > > > >
> > > > > > The HPB 2.0 supports read of varying sizes from 4KB to 512KB.
> > > > > > In the case of Read (<= 32KB) is supported as single HPB read.
> > > > > > In the case of Read (36KB ~ 512KB) is supported by as a 
> > > > > > combination
> > > > > > of
> > > > > > write buffer command and HPB read command to deliver more PPN.
> > > > > > The write buffer commands may not be issued immediately due to 
> > > > > > busy
> > > > > > tags.
> > > > > > To use HPB read more aggressively, the driver can requeue the 
> > > > > > write
> > > > > > buffer
> > > > > > command. The requeue threshold is implemented as timeout and can 
> > > > > > be
> > > > > > modified with requeue_timeout_ms entry in sysfs.
> > > > > >
> > > > > > Signed-off-by: Daejun Park <daejun7.park@xxxxxxxxxxx>
> > > > > > ---
> > > > > > +static struct attribute *hpb_dev_param_attrs[] = {
> > > > > > +        &dev_attr_requeue_timeout_ms.attr,
> > > > > > +        NULL,
> > > > > > +};
> > > > > > +
> > > > > > +struct attribute_group ufs_sysfs_hpb_param_group = {
> > > > > > +        .name = "hpb_param_sysfs",
> > > > > > +        .attrs = hpb_dev_param_attrs,
> > > > > > +};
> > > > > > +
> > > > > > +static int ufshpb_pre_req_mempool_init(struct ufshpb_lu *hpb)
> > > > > > +{
> > > > > > +        struct ufshpb_req *pre_req = NULL;
> > > > > > +        int qd = hpb->sdev_ufs_lu->queue_depth / 2;
> > > > > > +        int i, j;
> > > > > > +
> > > > > > +        INIT_LIST_HEAD(&hpb->lh_pre_req_free);
> > > > > > +
> > > > > > +        hpb->pre_req = kcalloc(qd, sizeof(struct ufshpb_req),
> > > > > > GFP_KERNEL);
> > > > > > +        hpb->throttle_pre_req = qd;
> > > > > > +        hpb->num_inflight_pre_req = 0;
> > > > > > +
> > > > > > +        if (!hpb->pre_req)
> > > > > > +                goto release_mem;
> > > > > > +
> > > > > > +        for (i = 0; i < qd; i++) {
> > > > > > +                pre_req = hpb->pre_req + i;
> > > > > > +                INIT_LIST_HEAD(&pre_req->list_req);
> > > > > > +                pre_req->req = NULL;
> > > > > > +                pre_req->bio = NULL;
> > > > >
> > > > > Why don't prepare bio as same as wb.m_page? Won't that save more 
> > > > > time
> > > > > for ufshpb_issue_pre_req()?
> > > >
> > > > It is pre_req pool. So although we prepare bio at this time, it just
> > > > only for first pre_req.
> > >
> > > I meant removing the bio_alloc() in ufshpb_issue_pre_req() and
> > > bio_put()
> > > in ufshpb_pre_req_compl_fn(). bios, in pre_req's case, just hold a
> > > page.
> > > So, prepare 16 (if queue depth is 32) bios here, just use them along
> > > with
> > > wb.m_page and call bio_reset() in ufshpb_pre_req_compl_fn(). Shall it
> > > work?
> >
> > If it works, you can even have the bio_add_pc_page() called here. 
> > Later
> > in
> > ufshpb_execute_pre_req(), you don't need to call
> > ufshpb_pre_req_add_bio_page(),
> > just call ufshpb_prep_entry() once instead - it save many repeated 
> > steps
> > for a
> > pre_req, and you don't even need to call bio_reset() in this case, 
> > since
> > for a
> > bio, nothing changes after it is binded with a specific page...
>
> Hi, Can Guo
>
> I tried the idea that you suggested, but it doesn't work properly.
> This optimization should be done next time for enhancement.

Can you elaborate please? Any error seen?

Per my understanding, in the case for pre_reqs, a bio is no different
from a page. Here it can reserve 16 pages for later use, which can be
done the same for bios.

This is not an enhancement, but a doubt - why not? Unless it is not 
doable.

Thanks,
Can Guo.

> Thanks
> Daejun
>
> > Can Guo.
> >
> > > Thanks,
> > > Can Guo.
> > >
> > > > After use it, it should be prepared bio at issue phase.
> > > >
> > > > Thanks,
> > > > Daejun
> > > >
> > > > > Thanks,
> > > > > Can Guo.
> > > > >
> > > > > > +
> > > > > > +                pre_req->wb.m_page = alloc_page(GFP_KERNEL |
> > > > > > __GFP_ZERO);
> > > > > > +                if (!pre_req->wb.m_page) {
> > > > > > +                        for (j = 0; j < i; j++)
> > > > > > +
> > > > > > __free_page(hpb->pre_req[j].wb.m_page);
> > > > > > +
> > > > > > +                        goto release_mem;
> > > > > > +                }
> > > > > > +                list_add_tail(&pre_req->list_req,
> > > > > > &hpb->lh_pre_req_free);
> > > > > > +        }
> > > > > > +
> > > > > > +        return 0;
> > > > > > +release_mem:
> > > > > > +        kfree(hpb->pre_req);
> > > > > > +        return -ENOMEM;
> > > > > > +}
> > > > > > +