linux-kernel - Re: [tip:timers/urgent] clockevents: tTack broadcast device mode change in tick_broadcast_switch_to

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Date:	Thu, 12 Apr 2012 09:27:35 +0800
From:	Alex Shi <lkml.alex@...il.com>
To:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	suresh.b.siddha@...el.com, santosh.shilimkar@...com,
	tglx@...utronix.de, Alex Shi <alex.shi@...el.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [tip:timers/urgent] clockevents: tTack broadcast device mode
 change in tick_broadcast_switch_to_oneshot()

On Tue, Apr 10, 2012 at 5:49 PM, tip-bot for Suresh Siddha
<suresh.b.siddha@...el.com> wrote:
> Commit-ID:  fa4da365bc7772c2cd6d5405bdf151612455f957
> Gitweb:     http://git.kernel.org/tip/fa4da365bc7772c2cd6d5405bdf151612455f957
> Author:     Suresh Siddha <suresh.b.siddha@...el.com>
> AuthorDate: Mon, 9 Apr 2012 15:41:44 -0700
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Tue, 10 Apr 2012 11:42:07 +0200
>
> clockevents: tTack broadcast device mode change in tick_broadcast_switch_to_oneshot()
>
> In the commit 77b0d60c5adf39c74039e2142a1d3cd1e4d53799,
> "clockevents: Leave the broadcast device in shutdown mode when not needed",
> we were bailing out too quickly in tick_broadcast_switch_to_oneshot(),
> with out tracking the broadcast device mode change to 'TICKDEV_MODE_ONESHOT'.
>
> This breaks the platforms which need broadcast device oneshot services during
> deep idle states. tick_broadcast_oneshot_control() thinks that it is
> in periodic mode and fails to take proper decisions based on the
> CLOCK_EVT_NOTIFY_BROADCAST_[ENTER, EXIT] notifications during deep
> idle entry/exit.
>
> Fix this by tracking the broadcast device mode as 'TICKDEV_MODE_ONESHOT',
> before leaving the broadcast HW device in shutdown mode if there are no active
> requests for the moment.
>

This patch recovered the loopback netperf testing on NHM machine, but
on SNB machine, It isn't need a broadcost timer at all.

Do you think it is better to remove oneshot broadcast on WSM/SNB machine?
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