linux-kernel - Re: [PATCH] tick: prefer a lower rating device only if it's CPU local device

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Message-ID: <alpine.DEB.2.21.1807031805560.1601@nanos.tec.linutronix.de>
Date:   Tue, 3 Jul 2018 18:08:19 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sudeep Holla <sudeep.holla@....com>
cc:     Kevin Hilman <khilman@...libre.com>,
        lkml <linux-kernel@...r.kernel.org>, fweisbec@...il.com,
        Arnd Bergmann <arnd@...db.de>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH] tick: prefer a lower rating device only if it's CPU
 local device

On Tue, 3 Jul 2018, Sudeep Holla wrote:
> On Tue, Jul 03, 2018 at 08:04:37AM -0700, Kevin Hilman wrote:
> > / # ls -l /sys/devices/system/clocksource
> > total 0
> > drwxr-xr-x    3 root     root             0 Jan  1 00:00 clocksource0
> > drwxr-xr-x    2 root     root             0 Jan  1 00:00 power
> > -rw-r--r--    1 root     root          4096 Jan  1 00:00 uevent
> > / # cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> > timer jiffies
> 
> Looks good.
> 
> > / # cat /sys/devices/system/clocksource/clocksource0/current_clocksource
> > timer
> >
> 
> OK, meson6 clocksource is active
> 
> > / # cat /sys/devices/system/clockevents/broadcast/current_device
> > meson6_tick
> 
> OK, it can support broadcast
> 
> > / # cat /sys/devices/system/clockevents/clockevent0/current_device
> > dummy_timer
> > / # cat /sys/devices/system/clockevents/clockevent1/current_device
> > dummy_timer
> > / # cat /sys/devices/system/clockevents/clockevent2/current_device
> > dummy_timer
> 
> But I can't understand why is dummy_timer the active event source and
> not meson6_tick. And you say this is working case ? Looks suspicious.

Because if it switches to broadcast mode then the meson timer cannot longer
be used as per cpu timer. It's broadcasting to all CPUs via the dummy timer.

Thanks,

	tglx