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Subject[PATCH v12 00/11] Early boot time stamps for x86
Date
changelog
---------
v12 - v11
- splitted time: replace read_boot_clock64() with
read_persistent_wall_and_boot_offset() into four patches
- Added two patches one fixes an existing bug with text_poke()
another one enables static branches early. Note, because I found
and fixed the text_poke() bug, enabling static branching became
super easy, as no changes to jump_label* is needed.
- Modified x86/tsc: use tsc early to use static branches early, and
thus native_sched_clock() is not changed at all.
v11 - v10
- Addressed all the comments from Thomas Gleixner.
- I added one more patch:
"x86/tsc: prepare for early sched_clock" which fixes a problem
that I discovered while testing. I am not particularly happy with
the fix, as it adds a new argument that is used only in one
place, but if you have a suggestion for a different approach on
how to address this problem please let me know.

v10 - v9
- Added another patch to this series that removes dependency
between KVM clock, and memblock allocator. The benefit is that
all clocks can now be initialized even earlier.
v9 - v8
- Addressed more comments from Dou Liyang

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()

The early boot time stamps were discussed recently in these threads:
http://lkml.kernel.org/r/1527672059-6225-1-git-send-email-feng.tang@intel.com
http://lkml.kernel.org/r/1527672059-6225-2-git-send-email-feng.tang@intel.com

I updated my series to the latest mainline and sending it again.

Peter mentioned he did not like patch 6,7, and we can discuss for a better
way to do that, but I think patches 1-5 can be accepted separetly, since
they already enable early timestamps on platforms where sched_clock() is
available early. Such as KVM.

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://paste.ubuntu.com/26133428/

After:
https://paste.ubuntu.com/26133523/

For 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 (7):
x86/tsc: remove tsc_disabled flag
time: sync read_boot_clock64() with persistent clock
x86/time: read_boot_clock64() implementation
sched: early boot clock
kvm/x86: remove kvm memblock dependency
x86/paravirt: add active_sched_clock to pv_time_ops
x86/tsc: use tsc early

Example 3:
http://lkml.kernel.org/r/20180615155733.1175-1-pasha.tatashin@oracle.com
- Needed early time stamps to show improvement

Pavel Tatashin (11):
x86: text_poke() may access uninitialized struct pages
x86: initialize static branching early
x86/tsc: redefine notsc to behave as tsc=unstable
kvm/x86: remove kvm memblock dependency
s390/time: add read_persistent_wall_and_boot_offset()
time: replace read_boot_clock64() with
read_persistent_wall_and_boot_offset()
s390/time: remove read_boot_clock64()
ARM/time: remove read_boot_clock64()
x86/tsc: prepare for early sched_clock
sched: early boot clock
x86/tsc: use tsc early

.../admin-guide/kernel-parameters.txt | 2 -
Documentation/x86/x86_64/boot-options.txt | 4 +-
arch/arm/kernel/time.c | 12 +---
arch/s390/kernel/time.c | 15 +++--
arch/x86/include/asm/text-patching.h | 1 +
arch/x86/kernel/alternative.c | 10 ++-
arch/x86/kernel/cpu/amd.c | 13 ++--
arch/x86/kernel/cpu/common.c | 38 ++++++-----
arch/x86/kernel/kvm.c | 1 +
arch/x86/kernel/kvmclock.c | 64 +++---------------
arch/x86/kernel/setup.c | 11 ++--
arch/x86/kernel/tsc.c | 65 ++++++++++---------
include/linux/timekeeping.h | 3 +-
kernel/sched/clock.c | 10 ++-
kernel/time/timekeeping.c | 61 ++++++++---------
15 files changed, 140 insertions(+), 170 deletions(-)

--
2.17.1

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