Date:   Mon, 4 Feb 2019 22:07:32 +0100
From:   Hans Holmberg <hans@...tronix.com>
To:     Javier González <javier@...igon.com>
Cc:     Matias Bjørling <mb@...htnvm.io>,
        Hans Holmberg <hans.holmberg@...xlabs.com>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

On Mon, Feb 4, 2019 at 9:14 AM Javier González <javier@...igon.com> wrote:
>
>
> > On 31 Jan 2019, at 21.10, Hans Holmberg <hans@...tronix.com> wrote:
> >
> > On Thu, Jan 31, 2019 at 5:33 PM Javier González <javier@...igon.com> wrote:
> >>> On 31 Jan 2019, at 11.41, Hans Holmberg <hans@...tronix.com> wrote:
> >>>
> >>> Hi Javier!
> >>>
> >>> How did you test this? I'm trying to add a test case to our testing framework.
> >>>
> >>> This is what i ran in qemu, and I got a hang (with this version of the patch)
> >>>
> >>> nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0
> >>
> >> I run several low configurations without problem. Can you share the qemu configuration and version?
> >
> > Of course!
> >
> > qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git
> > branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640)
> >
> > My geometry:
> > parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt
> > 24, cunits=0
>
> You are right, lmw_cunits=0 gives the problem.
>
> What about the following? If it goes through cijoe, I'll send a V3.

Please do send a V3 if it passes your testing.

Thanks!
Hans

>
> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
> index d4ca8c64ee0f..a6133b50ed9c 100644
> --- a/drivers/lightnvm/pblk-rb.c
> +++ b/drivers/lightnvm/pblk-rb.c
> @@ -45,10 +45,23 @@ void pblk_rb_free(struct pblk_rb *rb)
>  /*
>   * pblk_rb_calculate_size -- calculate the size of the write buffer
>   */
> -static unsigned int pblk_rb_calculate_size(unsigned int nr_entries)
> +static unsigned int pblk_rb_calculate_size(unsigned int nr_entries,
> +                                          unsigned int threshold)
>  {
> -       /* Alloc a write buffer that can at least fit 128 entries */
> -       return (1 << max(get_count_order(nr_entries), 7));
> +       unsigned int thr_sz = 1 << (get_count_order(threshold + NVM_MAX_VLBA));
> +       unsigned int max_sz = max(thr_sz, nr_entries);
> +       unsigned int max_io;
> +
> +       /* Alloc a write buffer that can (i) fit at least two split bios
> +        * (considering max I/O size NVM_MAX_VLBA, and (ii) guarantee that the
> +        * threshold will be respected
> +        */
> +       max_io = (1 << max((int)(get_count_order(max_sz)),
> +                               (int)(get_count_order(NVM_MAX_VLBA << 1))));
> +       if ((threshold + NVM_MAX_VLBA) >= max_io)
> +               max_io <<= 1;
> +
> +       return max_io;
>  }
>
>  /*
> @@ -67,12 +80,12 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold,
>         unsigned int alloc_order, order, iter;
>         unsigned int nr_entries;
>
> -       nr_entries = pblk_rb_calculate_size(size);
> +       nr_entries = pblk_rb_calculate_size(size, threshold);
>         entries = vzalloc(array_size(nr_entries, sizeof(struct pblk_rb_entry)));
>         if (!entries)
>                 return -ENOMEM;
>
> -       power_size = get_count_order(size);
> +       power_size = get_count_order(nr_entries);
>         power_seg_sz = get_count_order(seg_size);
>
>         down_write(&pblk_rb_lock);
> @@ -149,7 +162,7 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold,
>          * Initialize rate-limiter, which controls access to the write buffer
>          * by user and GC I/O
>          */
> -       pblk_rl_init(&pblk->rl, rb->nr_entries);
> +       pblk_rl_init(&pblk->rl, rb->nr_entries, threshold);
>
>         return 0;
>  }
> diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c
> index 76116d5f78e4..b014957dde0b 100644
> --- a/drivers/lightnvm/pblk-rl.c
> +++ b/drivers/lightnvm/pblk-rl.c
> @@ -207,7 +207,7 @@ void pblk_rl_free(struct pblk_rl *rl)
>         del_timer(&rl->u_timer);
>  }
>
> -void pblk_rl_init(struct pblk_rl *rl, int budget)
> +void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold)
>  {
>         struct pblk *pblk = container_of(rl, struct pblk, rl);
>         struct nvm_tgt_dev *dev = pblk->dev;
> @@ -217,7 +217,6 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
>         int sec_meta, blk_meta;
>         unsigned int rb_windows;
>
> -
>         /* Consider sectors used for metadata */
>         sec_meta = (lm->smeta_sec + lm->emeta_sec[0]) * l_mg->nr_free_lines;
>         blk_meta = DIV_ROUND_UP(sec_meta, geo->clba);
> @@ -234,7 +233,7 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
>         /* To start with, all buffer is available to user I/O writers */
>         rl->rb_budget = budget;
>         rl->rb_user_max = budget;
> -       rl->rb_max_io = budget >> 1;
> +       rl->rb_max_io = threshold ? (budget - threshold) : (budget - 1);
>         rl->rb_gc_max = 0;
>         rl->rb_state = PBLK_RL_HIGH;
>
> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> index 72ae8755764e..a6386d5acd73 100644
> --- a/drivers/lightnvm/pblk.h
> +++ b/drivers/lightnvm/pblk.h
> @@ -924,7 +924,7 @@ int pblk_gc_sysfs_force(struct pblk *pblk, int force);
>  /*
>   * pblk rate limiter
>   */
> -void pblk_rl_init(struct pblk_rl *rl, int budget);
> +void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold);
>  void pblk_rl_free(struct pblk_rl *rl);
>  void pblk_rl_update_rates(struct pblk_rl *rl);
>  int pblk_rl_high_thrs(struct pblk_rl *rl);
> --
> 2.17.1
>

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