linux-kernel - Re: [PATCH] nvme: explicitly disable APST on quirked devices

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Message-ID: <CALCETrV6HTiJ6E9dPKBZB2dykouqM0J5At_gQ3WC_itySnsiiA@mail.gmail.com>
Date:   Fri, 23 Jun 2017 10:17:58 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Lutomirski <luto@...nel.org>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvme: explicitly disable APST on quirked devices

On Thu, Jun 22, 2017 at 11:19 PM, Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
> A user reports APST is enabled, even when the NVMe is quirked or with
> option "default_ps_max_latency_us=0".
>
> The current logic will not set APST if the device is quirked. But the
> NVMe in question will enable APST automatically.
>
> Separate the logic "apst is supported" and "to enable apst", so we can
> use the latter one to explicitly disable APST at initialiaztion.
>
> BugLink: https://bugs.launchpad.net/bugs/1699004
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/nvme/host/core.c | 25 +++++++++++++++++--------
>  drivers/nvme/host/nvme.h |  1 +
>  2 files changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 0ddd6b9af7fc..c459d15d18f5 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1477,6 +1477,14 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl)
>         if (!ctrl->apsta)
>                 return;
>
> +       if (!ctrl->apst_enabled) {
> +               if (ctrl->state == NVME_CTRL_NEW ||
> +                   ctrl->state == NVME_CTRL_RESETTING)
> +                       dev_info(ctrl->device, "Disable APST at initialization\n");
> +               else
> +                       return;
> +       }
> +

Is this change really necessary?  ISTM that, if we want to optimize
the case where we're not changing anything, we should do it more
generally.

>         if (ctrl->npss > 31) {
>                 dev_warn(ctrl->device, "NPSS is invalid; not using APST\n");
>                 return;
> @@ -1486,7 +1494,7 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl)
>         if (!table)
>                 return;
>
> -       if (ctrl->ps_max_latency_us == 0) {
> +       if (ctrl->ps_max_latency_us == 0 || !ctrl->apst_enabled) {
>                 /* Turn off APST. */
>                 apste = 0;
>                 dev_dbg(ctrl->device, "APST disabled\n");
> @@ -1653,7 +1661,7 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
>         u64 cap;
>         int ret, page_shift;
>         u32 max_hw_sectors;
> -       u8 prev_apsta;
> +       bool prev_apst_enabled;
>
>         ret = ctrl->ops->reg_read32(ctrl, NVME_REG_VS, &ctrl->vs);
>         if (ret) {
> @@ -1721,16 +1729,17 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
>         ctrl->kas = le16_to_cpu(id->kas);
>
>         ctrl->npss = id->npss;
> -       prev_apsta = ctrl->apsta;
> +       ctrl->apsta = id->apsta;

So ctrl->apsta now means, literally, is APSTA set in the features.
This seems good.

> +       prev_apst_enabled = ctrl->apst_enabled;
>         if (ctrl->quirks & NVME_QUIRK_NO_APST) {
>                 if (force_apst && id->apsta) {
>                         dev_warn(ctrl->device, "forcibly allowing APST due to nvme_core.force_apst -- use at your own risk\n");
> -                       ctrl->apsta = 1;
> +                       ctrl->apst_enabled = true;
>                 } else {
> -                       ctrl->apsta = 0;
> +                       ctrl->apst_enabled = false;
>                 }
>         } else {
> -               ctrl->apsta = id->apsta;
> +               ctrl->apst_enabled = true;

Shouldn't this be ctrl->apst_enabled = id->apsta?

The way you have it could cause us to do the wrong thing if id->apsta
somehow changes between identifications.


>         memcpy(ctrl->psd, id->psd, sizeof(ctrl->psd));
>
> @@ -1760,9 +1769,9 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
>
>         kfree(id);
>
> -       if (ctrl->apsta && !prev_apsta)
> +       if (ctrl->apst_enabled && !prev_apst_enabled)
>                 dev_pm_qos_expose_latency_tolerance(ctrl->device);
> -       else if (!ctrl->apsta && prev_apsta)
> +       else if (!ctrl->apst_enabled && prev_apst_enabled)
>                 dev_pm_qos_hide_latency_tolerance(ctrl->device);

This is also wrong unless you make the change above, I think.

--Andy