[PATCH v8 0/6] Early boot time stamps for x86

[Pavel Tatashin <pasha.tatashin@oracle.com>]

changelog
---------
v8 - v7
	- Addressed comments from Dou Liyang:
	- Moved tsc_early_init() and tsc_early_fini() to be all inside
	  tsc.c, and changed them to be static.
	- Removed warning when notsc parameter is used.
	- Merged with:
	  https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

v7 - v6
	- Removed tsc_disabled flag, now notsc is equivalent of
	  tsc=unstable
	- Simplified changes to sched/clock.c, by removing the
	  sched_clock_early() and friends as requested by Peter Zijlstra.
	  We know always use sched_clock()
	- Modified x86 sched_clock() to return either early boot time or
	  regular.
	- Added another example why ealry boot time is important

v5 - v6
	- Added a new patch:
		time: sync read_boot_clock64() with persistent clock
	  Which fixes missing __init macro, and enabled time discrepancy
	  fix that was noted by Thomas Gleixner
	- Split "x86/time: read_boot_clock64() implementation" into a
	  separate patch
v4 - v5
	- Fix compiler warnings on systems with stable clocks.

v3 - v4
	- Fixed tsc_early_fini() call to be in the 2nd patch as reported
	  by Dou Liyang
	- Improved comment before __use_sched_clock_early to explain why
	  we need both booleans.
	- Simplified valid_clock logic in read_boot_clock64().

v2 - v3
	- Addressed comment from Thomas Gleixner
	- Timestamps are available a little later in boot but still much
	  earlier than in mainline. This significantly simplified this
	  work.

v1 - v2
	In patch "x86/tsc: tsc early":
	- added tsc_adjusted_early()
	- fixed 32-bit compile error use do_div()

Adding early boot time stamps support for x86 machines.
SPARC patches for early boot time stamps are already integrated into
mainline linux.

Sample output
-------------
Before:
https://hastebin.com/jadaqukubu.scala

After:
https://hastebin.com/nubipozacu.scala

For more exaples how early time stamps are used, see this work:

Example 1:
https://lwn.net/Articles/734374/
- Without early boot time stamps we would not know about the extra time
  that is spent zeroing struct pages early in boot even when deferred
  page initialization.

Example 2:
https://patchwork.kernel.org/patch/10021247/
- If early boot timestamps were available, the engineer who introduced
  this bug would have noticed the extra time that is spent early in boot.

Pavel Tatashin (6):
  x86/tsc: remove tsc_disabled flag
  time: sync read_boot_clock64() with persistent clock
  x86/time: read_boot_clock64() implementation
  sched: early boot clock
  x86/paravirt: add active_sched_clock to pv_time_ops
  x86/tsc: use tsc early

 arch/arm/kernel/time.c                |   2 +-
 arch/s390/kernel/time.c               |   2 +-
 arch/x86/include/asm/paravirt.h       |   2 +-
 arch/x86/include/asm/paravirt_types.h |   1 +
 arch/x86/kernel/paravirt.c            |   1 +
 arch/x86/kernel/time.c                |  30 ++++++++++
 arch/x86/kernel/tsc.c                 | 104 ++++++++++++++++++++++++++++------
 arch/x86/xen/time.c                   |   7 ++-
 include/linux/timekeeping.h           |   7 +--
 kernel/sched/clock.c                  |  10 +++-
 kernel/time/timekeeping.c             |   8 ++-
 11 files changed, 144 insertions(+), 30 deletions(-)

-- 
2.15.0