LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Kevin Hilman <khilman@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Preeti U Murthy <preeti@linux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH 1/3] clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state
Date: Mon, 06 Apr 2015 14:26:43 -0700	[thread overview]
Message-ID: <7h1tjxx818.fsf@deeprootsystems.com> (raw)
In-Reply-To: <c283d8555b670c4952ceef5782ebe743fbd8a373.1427475606.git.viresh.kumar@linaro.org> (Viresh Kumar's message of "Fri, 27 Mar 2015 22:44:27 +0530")

Viresh Kumar <viresh.kumar@linaro.org> writes:

> When no timers/hrtimers are pending, the expiry time is set to a special value:
> 'KTIME_MAX'. This normally happens with NO_HZ_{IDLE|FULL} in both LOWRES/HIGHRES
> modes.
>
> When 'expiry == KTIME_MAX', we either cancel the 'tick-sched' hrtimer
> (NOHZ_MODE_HIGHRES) or skip reprogramming clockevent device (NOHZ_MODE_LOWRES).
> But, the clockevent device is already reprogrammed from the tick-handler for
> next tick.
>
> As the clock event device is programmed in ONESHOT mode it will at least fire
> one more time (unnecessarily). Timers on few implementations (like
> arm_arch_timer, etc.) only support PERIODIC mode and their drivers emulate
> ONESHOT over that. Which means that on these platforms we will get spurious
> interrupts periodically (at last programmed interval rate, normally tick rate).
>
> In order to avoid spurious interrupts, the clockevent device should be stopped
> or its interrupts should be masked.
>
> A simple (yet hacky) solution to get this fixed could be: update
> hrtimer_force_reprogram() to always reprogram clockevent device and update
> clockevent drivers to STOP generating events (or delay it to max time) when
> 'expires' is set to KTIME_MAX. But the drawback here is that every clockevent
> driver has to be hacked for this particular case and its very easy for new ones
> to miss this.
>
> However, Thomas suggested to add an optional state ONESHOT_STOPPED to solve this
> problem: lkml.org/lkml/2014/5/9/508.
>
> This patch adds support for ONESHOT_STOPPED state in clockevents core. It will
> only be available to drivers that implement the state-specific callbacks instead
> of the legacy ->set_mode() callback.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Reviewed-by: Kevin Hilman <khilman@linaro.org>

with a minor nit...

[...]

> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
> index 73689df1e4b8..04f6c3433f8e 100644
> --- a/kernel/time/clockevents.c
> +++ b/kernel/time/clockevents.c
> @@ -138,6 +138,17 @@ static int __clockevents_set_state(struct clock_event_device *dev,
>  			return -ENOSYS;
>  		return dev->set_state_oneshot(dev);
>  
> +	case CLOCK_EVT_STATE_ONESHOT_STOPPED:
> +		/* Core internal bug */

This comment is not useful at all (nor are all the other ones already in
this file.)  IMO, the comment should say something like:
"ONESHOT_STOPPED is only valid when currently in the ONESHOT state." or
something similar.


> +		if (WARN_ONCE(dev->state != CLOCK_EVT_STATE_ONESHOT,
> +			      "Current state: %d\n", dev->state))

Similarily this output will not be useful, and should say something
like: "Can only enter ONESHOT_STOPPED from ONESHOT.  Current state: %d\n".

> +			return -EINVAL;
> +
> +		if (dev->set_state_oneshot_stopped)
> +			return dev->set_state_oneshot_stopped(dev);
> +		else
> +			return -ENOSYS;
> +
>  	default:
>  		return -ENOSYS;
>  	}

Kevin

  parent reply	other threads:[~2015-04-06 21:26 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-27 17:14 [PATCH 0/3] clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED Viresh Kumar
2015-03-27 17:14 ` [PATCH 1/3] clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state Viresh Kumar
2015-03-30  5:49   ` Preeti U Murthy
2015-04-06 21:26   ` Kevin Hilman [this message]
2015-03-27 17:14 ` [PATCH 2/3] clockevents: Restart clockevent device before using it again Viresh Kumar
2015-03-30  5:52   ` Preeti U Murthy
2015-04-02 13:34   ` Peter Zijlstra
2015-04-02 13:50     ` Viresh Kumar
2015-04-02 15:06       ` Peter Zijlstra
2015-04-02 16:04         ` Ingo Molnar
2015-03-27 17:14 ` [PATCH 3/3] clockevents: Switch state to ONESHOT_STOPPED for unused clockevent devices Viresh Kumar
2015-03-30  5:50   ` Preeti U Murthy
2015-04-02 13:37   ` Peter Zijlstra
2015-04-02 13:51     ` Viresh Kumar

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=7h1tjxx818.fsf@deeprootsystems.com \
    --to=khilman@kernel.org \
    --cc=daniel.lezcano@linaro.org \
    --cc=fweisbec@gmail.com \
    --cc=linaro-kernel@lists.linaro.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=preeti@linux.vnet.ibm.com \
    --cc=tglx@linutronix.de \
    --cc=viresh.kumar@linaro.org \
    --subject='Re: [PATCH 1/3] clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).