linux-toradex.git/kernel/time/timekeeping.c, branch v2.6.32.52

timekeeping: add arch_offset hook to ktime_get functions

2011-12-09T17:21:38+00:00

commit d004e024058a0eaca097513ce62cbcf978913e0a upstream.

ktime_get and ktime_get_ts were calling timekeeping_get_ns()
but later they were not calling arch_gettimeoffset() so architectures
using this mechanism returned 0 ns when calling these functions.

This happened for example when running Busybox's ping which calls
syscall(__NR_clock_gettime, CLOCK_MONOTONIC, ts) which eventually
calls ktime_get. As a result the returned ping travel time was zero.

Signed-off-by: Hector Palacios 
Signed-off-by: John Stultz 
Signed-off-by: Greg Kroah-Hartman

time: Compensate for rounding on odd-frequency clocksources

2011-06-23T22:24:09+00:00

commit a386b5af8edda1c742ce9f77891e112eefffc005 upstream.

When the clocksource is not a multiple of HZ, the clock will be off.  For
acpi_pm, HZ=1000 the error is 127.111 ppm:

The rounding of cycle_interval ends up generating a false error term in
ntp_error accumulation since xtime_interval is not exactly 1/HZ.  So, we
subtract out the error caused by the rounding.

This has been visible since 2.6.32-rc2
	commit a092ff0f90cae22b2ac8028ecd2c6f6c1a9e4601
	time: Implement logarithmic time accumulation
That commit raised NTP_INTERVAL_FREQ and exposed the rounding error.

testing tool: http://n1.taur.dk/permanent/testpmt.c
Also tested with ntpd and a frequency counter.

Signed-off-by: Kasper Pedersen 
Acked-by: john stultz 
Cc: John Kacur 
Cc: Clark Williams 
Cc: Martin Schwidefsky 
Signed-off-by: Andrew Morton 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Will Tisdale 
Signed-off-by: Greg Kroah-Hartman

Fix time() inconsistencies caused by intermediate xtime_cache values being read

2011-05-23T18:20:15+00:00

Currently with 2.6.32-longterm, its possible for time() to occasionally
return values one second earlier then the previous time() call.

This happens because update_xtime_cache() does:
	xtime_cache = xtime;
	timespec_add_ns(&xtime_cache, nsec);

Its possible that xtime is 1sec,999msecs, and nsecs is 1ms, resulting in
a xtime_cache that is 2sec,0ms.

get_seconds() (which is used by sys_time()) does not take the
xtime_lock, which is ok as the xtime.tv_sec value is a long and can be
atomically read safely.

The problem occurs the next call to update_xtime_cache() if xtime has
not increased:
	/* This sets xtime_cache back to 1sec, 999msec */
	xtime_cache = xtime; 
	/* get_seconds, calls here, and sees a 1second inconsistency */
	timespec_add_ns(&xtime_cache, nsec);


In order to resolve this, we could add locking to get_seconds(), but it
needs to be lock free, as it is called from the machine check handler,
opening a possible deadlock.

So instead, this patch introduces an intermediate value for the
calculations, so that we only assign xtime_cache once with the correct
time, using ACCESS_ONCE to make sure the compiler doesn't optimize out
any intermediate values.

The xtime_cache manipulations were removed with 2.6.35, so that kernel
and later do not need this change.

In 2.6.33 and 2.6.34 the logarithmic accumulation should make it so
xtime is updated each tick, so it is unlikely that two updates to
xtime_cache could occur while the difference between xtime and
xtime_cache crosses the second boundary. However, the paranoid might
want to pull this into 2.6.33/34-longterm just to be sure.

Thanks to Stephen for helping finally narrow down the root cause and
many hours of help with testing and validation. Also thanks to Max,
Andi, Eric and Paul for review of earlier attempts and helping clarify
what is possible with regard to out of order execution.

Acked-by: Eric Dumazet 
Signed-off-by: John Stultz 
Signed-off-by: Greg Kroah-Hartman

timekeeping: Fix clock_gettime vsyscall time warp

2010-08-13T20:20:13+00:00

commit 0696b711e4be45fa104c12329f617beb29c03f78 upstream.

Since commit 0a544198 "timekeeping: Move NTP adjusted clock multiplier
to struct timekeeper" the clock multiplier of vsyscall is updated with
the unmodified clock multiplier of the clock source and not with the
NTP adjusted multiplier of the timekeeper.

This causes user space observerable time warps:
new CLOCK-warp maximum: 120 nsecs,  00000025c337c537 -> 00000025c337c4bf

Add a new argument "mult" to update_vsyscall() and hand in the
timekeeping internal NTP adjusted multiplier.

Signed-off-by: Lin Ming 
Cc: "Zhang Yanmin" 
Cc: Martin Schwidefsky 
Cc: Benjamin Herrenschmidt 
Cc: Tony Luck 
LKML-Reference: <1258436990.17765.83.camel@minggr.sh.intel.com>
Signed-off-by: Thomas Gleixner 
Signed-off-by: Kurt Garloff 
Signed-off-by: Greg Kroah-Hartman

Export the symbol of getboottime and mmonotonic_to_bootbased

2010-02-23T15:37:52+00:00

commit c93d89f3dbf0202bf19c07960ca8602b48c2f9a0 upstream.

Export getboottime and monotonic_to_bootbased in order to let them
could be used by following patch.

Signed-off-by: Jason Wang 
Signed-off-by: Marcelo Tosatti 
Signed-off-by: Greg Kroah-Hartman

nohz: Prevent clocksource wrapping during idle

2010-01-28T23:01:12+00:00

commit 98962465ed9e6ea99c38e0af63fe1dcb5a79dc25 upstream.

The dynamic tick allows the kernel to sleep for periods longer than a
single tick, but it does not limit the sleep time currently. In the
worst case the kernel could sleep longer than the wrap around time of
the time keeping clock source which would result in losing track of
time.

Prevent this by limiting it to the safe maximum sleep time of the
current time keeping clock source. The value is calculated when the
clock source is registered.

[ tglx: simplified the code a bit and massaged the commit msg ]

Signed-off-by: Jon Hunter 
Cc: John Stultz 
LKML-Reference: <1250617512-23567-2-git-send-email-jon-hunter@ti.com>
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

headers: remove sched.h from interrupt.h

2009-10-11T18:20:58+00:00

After m68k's task_thread_info() doesn't refer to current,
it's possible to remove sched.h from interrupt.h and not break m68k!
Many thanks to Heiko Carstens for allowing this.

Signed-off-by: Alexey Dobriyan

timekeeping: Fix invalid getboottime() value

2009-08-25T07:09:02+00:00

Don't use timespec_add_safe() with wall_to_monotonic, because
wall_to_monotonic has negative values which will cause overflow
in timespec_add_safe(). That makes btime in /proc/stat invalid.

Signed-off-by: Hiroshi Shimamoto 
Cc: Martin Schwidefsky 
Cc: John Stultz 
Cc: Daniel Walker 
LKML-Reference: <4A937FDE.4050506@ct.jp.nec.com>
Signed-off-by: Ingo Molnar

time: Introduce CLOCK_REALTIME_COARSE

2009-08-21T19:43:46+00:00

After talking with some application writers who want very fast, but not
fine-grained timestamps, I decided to try to implement new clock_ids
to clock_gettime(): CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE
which returns the time at the last tick. This is very fast as we don't
have to access any hardware (which can be very painful if you're using
something like the acpi_pm clocksource), and we can even use the vdso
clock_gettime() method to avoid the syscall. The only trade off is you
only get low-res tick grained time resolution.

This isn't a new idea, I know Ingo has a patch in the -rt tree that made
the vsyscall gettimeofday() return coarse grained time when the
vsyscall64 sysctrl was set to 2. However this affects all applications
on a system.

With this method, applications can choose the proper speed/granularity
trade-off for themselves.

Signed-off-by: John Stultz 
Cc: Andi Kleen 
Cc: nikolag@ca.ibm.com
Cc: Darren Hart 
Cc: arjan@infradead.org
Cc: jonathan@jonmasters.org
LKML-Reference: <1250734414.6897.5.camel@localhost.localdomain>
Signed-off-by: Thomas Gleixner

timekeeping: Introduce read_boot_clock

2009-08-15T08:55:47+00:00

Add the new function read_boot_clock to get the exact time the system
has been started. For architectures without support for exact boot
time a new weak function is added that returns 0.  Use the exact boot
time to initialize wall_to_monotonic, or xtime if the read_boot_clock
returned 0.

Signed-off-by: Martin Schwidefsky 
Cc: Ingo Molnar 
Acked-by: John Stultz 
Cc: Daniel Walker 
LKML-Reference: <20090814134811.296703241@de.ibm.com>
Signed-off-by: Thomas Gleixner