Commit Graph

11 Commits

Author SHA1 Message Date
Salman Qazi 9993bc635d sched/x86: Fix overflow in cyc2ns_offset
When a machine boots up, the TSC generally gets reset.  However,
when kexec is used to boot into a kernel, the TSC value would be
carried over from the previous kernel.  The computation of
cycns_offset in set_cyc2ns_scale is prone to an overflow, if the
machine has been up more than 208 days prior to the kexec.  The
overflow happens when we multiply *scale, even though there is
enough room to store the final answer.

We fix this issue by decomposing tsc_now into the quotient and
remainder of division by CYC2NS_SCALE_FACTOR and then performing
the multiplication separately on the two components.

Refactor code to share the calculation with the previous
fix in __cycles_2_ns().

Signed-off-by: Salman Qazi <sqazi@google.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Turner <pjt@google.com>
Cc: john stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/20120310004027.19291.88460.stgit@dungbeetle.mtv.corp.google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2012-03-13 16:27:51 +01:00
Salman Qazi 4cecf6d401 sched, x86: Avoid unnecessary overflow in sched_clock
(Added the missing signed-off-by line)

In hundreds of days, the __cycles_2_ns calculation in sched_clock
has an overflow.  cyc * per_cpu(cyc2ns, cpu) exceeds 64 bits, causing
the final value to become zero.  We can solve this without losing
any precision.

We can decompose TSC into quotient and remainder of division by the
scale factor, and then use this to convert TSC into nanoseconds.

Signed-off-by: Salman Qazi <sqazi@google.com>
Acked-by: John Stultz <johnstul@us.ibm.com>
Reviewed-by: Paul Turner <pjt@google.com>
Cc: stable@kernel.org
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111115221121.7262.88871.stgit@dungbeetle.mtv.corp.google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-11-16 19:51:25 +01:00
Don Zickus 072b198a4a x86, nmi_watchdog: Remove all stub function calls from old nmi_watchdog
Now that the bulk of the old nmi_watchdog is gone, remove all
the stub variables and hooks associated with it.

This touches lots of files mainly because of how the io_apic
nmi_watchdog was implemented.  Now that the io_apic nmi_watchdog
is forever gone, remove all its fingers.

Most of this code was not being exercised by virtue of
nmi_watchdog != NMI_IO_APIC, so there shouldn't be anything to
risky here.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: fweisbec@gmail.com
Cc: gorcunov@openvz.org
LKML-Reference: <1289578944-28564-3-git-send-email-dzickus@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 09:08:23 +01:00
Thomas Gleixner 2d826404f0 x86: Move tsc_calibration to x86_init_ops
TSC calibration is modified by the vmware hypervisor and paravirt by
separate means. Moorestown wants to add its own calibration routine as
well. So make calibrate_tsc a proper x86_init_ops function and
override it by paravirt or by the early setup of the vmware
hypervisor.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2009-08-31 09:35:47 +02:00
Thomas Gleixner 64fcbac1f3 x86: Simplify timer_ack magic in time_32.c
Let the compiler optimize the timer_ack magic away in the 32bit timer
interrupt and put the same code into time_64.c. It's optimized out for
CONFIG_X86_IO_APIC on 32bit and for 64bit because timer_ack is const 0
in both cases.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2009-08-31 09:35:46 +02:00
Thomas Gleixner 845b3944bb x86: Add timer_init to x86_init_ops
The timer init code is convoluted with several quirks and the paravirt
timer chooser. Figuring out which code path is actually taken is not
for the faint hearted.

Move the numaq TSC quirk to tsc_pre_init x86_init_ops function and
replace the paravirt time chooser and the remaining x86 quirk with a
simple x86_init_ops function.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2009-08-31 09:35:46 +02:00
Peter Zijlstra 84599f8a59 sched, x86: Fix cpufreq + sched_clock() TSC scaling
For freqency dependent TSCs we only scale the cycles, we do not account
for the discrepancy in absolute value.

Our current formula is: time = cycles * mult

(where mult is a function of the cpu-speed on variable tsc machines)

Suppose our current cycle count is 10, and we have a multiplier of 5,
then our time value would end up being 50.

Now cpufreq comes along and changes the multiplier to say 3 or 7,
which would result in our time being resp. 30 or 70.

That means that we can observe random jumps in the time value due to
frequency changes in both fwd and bwd direction.

So what this patch does is change the formula to:

  time = cycles * frequency + offset

And we calculate offset so that time_before == time_after, thereby
ridding us of these jumps in time.

[ Impact: fix/reduce sched_clock() jumps across frequency changing events ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Chucked-on-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2009-06-17 16:03:54 +02:00
Stephen Rothwell 25c1a411e8 x86: fix mismerge in arch/x86/include/asm/timer.h
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-03-30 10:10:49 -07:00
Ingo Molnar 8e6dafd6c7 x86: refactor x86_quirks support
Impact: cleanup

Make x86_quirks support more transparent. The highlevel
methods are now named:

  extern void x86_quirk_pre_intr_init(void);
  extern void x86_quirk_intr_init(void);

  extern void x86_quirk_trap_init(void);

  extern void x86_quirk_pre_time_init(void);
  extern void x86_quirk_time_init(void);

This makes it clear that if some platform extension has to
do something here that it is considered ... weird, and is
discouraged.

Also remove arch_hooks.h and move it into setup.h (and other
header files where appropriate).

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-23 00:08:11 +01:00
H. Peter Anvin 1965aae3c9 x86: Fix ASM_X86__ header guards
Change header guards named "ASM_X86__*" to "_ASM_X86_*" since:

a. the double underscore is ugly and pointless.
b. no leading underscore violates namespace constraints.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2008-10-22 22:55:23 -07:00
Al Viro bb8985586b x86, um: ... and asm-x86 move
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
2008-10-22 22:55:20 -07:00