linux-kernel - Re: [PATCH 3/6] nfit/ars: Allow root to busy-poll the ARS state machine

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Message-ID: <CAPcyv4g83aNP_CF+hygCEQ=9dRL9beC7vGGLQDg9=rMy2+nPfQ@mail.gmail.com>
Date:   Thu, 14 Feb 2019 12:27:02 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-nvdimm <linux-nvdimm@...ts.01.org>
Cc:     Erwin Tsaur <erwin.tsaur@...cle.com>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] nfit/ars: Allow root to busy-poll the ARS state machine

On Thu, Feb 14, 2019 at 12:23 PM Dan Williams <dan.j.williams@...el.com> wrote:
>
> The ARS implementation implements exponential back-off on the poll
> interval to prevent high-frequency access to the DIMM / platform
> interface. Depending on when the ARS completes the poll interval may
> exceed the completion event by minutes. Allow root to reset the timeout
> each time it probes the status. A one-second timeout is still enforced,
> but root can otherwise can control the poll interval.
>
> Reported-by: Erwin Tsaur <erwin.tsaur@...cle.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  drivers/acpi/nfit/core.c |    6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
> index 934be96dc149..5ec0e19760ea 100644
> --- a/drivers/acpi/nfit/core.c
> +++ b/drivers/acpi/nfit/core.c
> @@ -1328,6 +1328,12 @@ static ssize_t scrub_show(struct device *dev,
>                 rc = sprintf(buf, "%d%s", acpi_desc->scrub_count,
>                                 acpi_desc->scrub_busy
>                                 && !acpi_desc->cancel ? "+\n" : "\n");
> +               /* Allow an admin to poll the busy state at a higher rate */
> +               if (acpi_desc->scrub_busy && !acpi_desc->cancel
> +                               && capable(CAP_SYS_RAWIO)) {
> +                       acpi_desc->scrub_tmo = 1;
> +                       queue_delayed_work(nfit_wq, &acpi_desc->dwork, HZ);

Whoops, just realized this should be mod_delayed_work().
queue_delayed_work() is a nop if the work is already scheduled. v2
inbound.