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

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