Impact: fix incorrectly marked unstable TSC clock

Patch (commit 0d12cdd5 "sched: improve sched_clock() performance") has
a regression on one of the test systems here.

With the patch, I see:

 checking TSC synchronization [CPU#0 -> CPU#1]:
 Measured 28 cycles TSC warp between CPUs, turning off TSC clock.
 Marking TSC unstable due to check_tsc_sync_source failed

Whereas, without the patch syncs pass fine on all CPUs:

 checking TSC synchronization [CPU#0 -> CPU#1]: passed.

Due to this, TSC is marked unstable, when it is not actually unstable.
This is because syncs in check_tsc_wrap() goes away due to this commit.

As per the discussion on this thread, correct way to fix this is to add
explicit syncs as below?
Signed-off-by: NVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Use WARN() instead of a printk+WARN_ON() pair; this way the message
becomes part of the warning section for better reporting/collection.
This also allowed the folding of some if()'s into the WARN()
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Cc: akpm@linux-foundation.org
Signed-off-by: NIngo Molnar <mingo@elte.hu>

add warning to check_tsc_warp() - if get_cycles() does not progress.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

100 million max # of loops is a bit too much - reduce it to 10 million.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

rdtsc is now speculation-safe, so no need for the sync variants of
the APIs.

[ mingo@elte.hu: removed the nsec_barrier() complication. ]
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

s2ram recently became useful here, except for the kernel's annoying
habit of disabling my P4's perfectly good TSC.

[  107.894470] CPU 1 is now offline
[  107.894474] SMP alternatives: switching to UP code
[  107.895832] CPU0 attaching sched-domain:
[  107.895836]  domain 0: span 1
[  107.895838]   groups: 1
[  107.896097] CPU1 is down
[    3.726156] Intel machine check architecture supported.
[    3.726165] Intel machine check reporting enabled on CPU#0.
[    3.726167] CPU0: Intel P4/Xeon Extended MCE MSRs (12) available
[    3.726170] CPU0: Thermal monitoring enabled
[    3.726175] Back to C!
[    3.726708] Force enabled HPET at resume
[    3.726775] Enabling non-boot CPUs ...
[    3.727049] CPU0 attaching NULL sched-domain.
[    3.727165] SMP alternatives: switching to SMP code
[    3.727858] Booting processor 1/1 eip 3000
[    3.727862] CPU 1 irqstacks, hard=b042f000 soft=b042d000
[    3.738173] Initializing CPU#1
[    3.798912] Calibrating delay using timer specific routine.. 5986.12 BogoMIPS (lpj=2993061)
[    3.798920] CPU: After generic identify, caps: bfebfbff 00000000 00000000 00000000 00004400 00000000 00000000 00000000
[    3.798931] CPU: Trace cache: 12K uops, L1 D cache: 8K
[    3.798934] CPU: L2 cache: 512K
[    3.798936] CPU: Physical Processor ID: 0
[    3.798938] CPU: After all inits, caps: bfebfbff 00000000 00000000 0000b080 00004400 00000000 00000000 00000000
[    3.798946] Intel machine check architecture supported.
[    3.798952] Intel machine check reporting enabled on CPU#1.
[    3.798955] CPU1: Intel P4/Xeon Extended MCE MSRs (12) available
[    3.798959] CPU1: Thermal monitoring enabled
[    3.799161] CPU1: Intel(R) Pentium(R) 4 CPU 3.00GHz stepping 09
[    3.799187] checking TSC synchronization [CPU#0 -> CPU#1]:
[    3.819181] Measured 63588552840 cycles TSC warp between CPUs, turning off TSC clock.
[    3.819184] Marking TSC unstable due to: check_tsc_sync_source failed.

If check_tsc_warp() is called after initial boot, and the TSC has in the
meantime been set (BIOS, user, silicon, elves) to a value lower than the
last stored/stale value, we blame the TSC.  Reset to pristine condition
after every test.
Signed-off-by: NMike Galbraith <efault@gmx.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

Since the x86 merge, lots of files that referenced their own filenames
are no longer correct.  Rather than keep them up to date, just delete
them, as they add no real value.

Additionally:
- fix up comment formatting in scx200_32.c
- Remove a credit from myself in setup_64.c from a time when we had no SCM
- remove longwinded history from tsc_32.c which can be figured out from
  git.
Signed-off-by: NDave Jones <davej@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

make the TSC synchronization code more robust, and unify it between x86_64 and
i386.

The biggest change is the removal of the 'fix up TSCs' code on x86_64 and
i386, in some rare cases it was /causing/ time-warps on SMP systems.

The new code only checks for TSC asynchronity - and if it can prove a
time-warp (if it can observe the TSC going backwards when going from one CPU
to another within a critical section), then the TSC clock-source is turned
off.

The TSC synchronization-checking code also got moved into a separate file.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>