linux_old1/include
Thomas Gleixner 332962f2c8 clocksource: Reselect clocksource when watchdog validated high-res capability
Up to commit 5d33b883a (clocksource: Always verify highres capability)
we had no sanity check when selecting a clocksource, which prevented
that a non highres capable clocksource is used when the system already
switched to highres/nohz mode.

The new sanity check works as Alex and Tim found out. It prevents the
TSC from being used. This happens because on x86 the boot process
looks like this:

 tsc_start_freqency_validation(TSC);
 clocksource_register(HPET);
 clocksource_done_booting();
	clocksource_select()
		Selects HPET which is valid for high-res

 switch_to_highres();

 clocksource_register(TSC);
 	TSC is not selected, because it is not yet
	flagged as VALID_HIGH_RES

 clocksource_watchdog()
	Validates TSC for highres, but that does not make TSC
	the current clocksource.

Before the sanity check was added, we installed TSC unvalidated which
worked most of the time. If the TSC was really detected as unstable,
then the unstable logic removed it and installed HPET again.

The sanity check is correct and needed. So the watchdog needs to kick
a reselection of the clocksource, when it qualifies TSC as a valid
high res clocksource.

To solve this, we mark the clocksource which got the flag
CLOCK_SOURCE_VALID_FOR_HRES set by the watchdog with an new flag
CLOCK_SOURCE_RESELECT and trigger the watchdog thread. The watchdog
thread evaluates the flag and invokes clocksource_select() when set.

To avoid that the clocksource_done_booting() code, which is about to
install the first real clocksource anyway, needs to go through
clocksource_select and tick_oneshot_notify() pointlessly, split out
the clocksource_watchdog_kthread() list walk code and invoke the
select/notify only when called from clocksource_watchdog_kthread().

So clocksource_done_booting() can utilize the same splitout code
without the select/notify invocation and the clocksource_mutex
unlock/relock dance.

Reported-and-tested-by: Alex Shi <alex.shi@intel.com>
Cc: Hans Peter Anvin <hpa@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Andi Kleen <andi.kleen@intel.com>
Tested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1307042239150.11637@ionos.tec.linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2013-07-05 11:09:28 +02:00
..
acpi ACPI / dock / PCI: Synchronous handling of dock events for PCI devices 2013-06-24 11:22:53 +02:00
asm-generic Merge branch 'fixes' of git://git.kernel.org/pub/scm/virt/kvm/kvm 2013-06-11 11:16:43 -07:00
clocksource ARM: late Exynos multiplatform changes 2013-05-07 11:28:42 -07:00
crypto crypto: sha512 - Expose generic sha512 routine to be callable from other modules 2013-04-25 21:00:57 +08:00
drm Merge branch 'drm-radeon-sun-hainan' of git://people.freedesktop.org/~airlied/linux 2013-05-21 08:50:57 -07:00
dt-bindings
keys
linux clocksource: Reselect clocksource when watchdog validated high-res capability 2013-07-05 11:09:28 +02:00
math-emu
media Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media 2013-06-18 06:25:08 -10:00
memory
misc
net ip_tunnel: remove __net_init/exit from exported functions 2013-06-13 03:00:59 -07:00
pcmcia
ras
rdma
rxrpc
scsi Merge branch 'postmerge' into for-linus 2013-05-10 07:54:01 -07:00
sound ASoC: dapm: Treat DAI widgets like AIF widgets for power 2013-06-07 15:54:50 +01:00
target target: Propigate up ->cmd_kref put return via transport_generic_free_cmd 2013-05-31 01:21:23 -07:00
trace Fixed regressions (two stability regressions and a performance 2013-05-14 09:30:54 -07:00
uapi netlink: export netlink_diag.h header 2013-06-19 18:30:27 -07:00
video Merge branch 'fbdev-3.10-fixes' of git://gitorious.org/linux-omap-dss2/linux into linux-fbdev/for-3.10-fixes 2013-05-29 17:00:34 +08:00
xen xenbus: delay xenbus frontend resume if xenstored is not running 2013-05-29 09:04:19 -04:00
Kbuild UAPI: remove empty Kbuild files 2013-04-30 17:04:09 -07:00