linux-kernel - Re: [PATCH v9 0/6] Early boot time stamps for x86

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Date:   Wed, 6 Dec 2017 13:11:14 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Dou Liyang <douly.fnst@...fujitsu.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Steve Sistare <steven.sistare@...cle.com>, mingo@...hat.com,
        hpa@...or.com, prarit@...hat.com,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        schwidefsky@...ibm.com, linux@...linux.org.uk,
        heiko.carstens@...ibm.com, sboyd@...eaurora.org,
        John Stultz <john.stultz@...aro.org>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v9 0/6] Early boot time stamps for x86

Hi Thomas and Peter,

I have a few minor changes to this patch series
Such as include: Reviewed-by: Dou Liyang <douly.fnst@...fujitsu.com>
And a couple minor cosmetic/description changes, but I would like to
get your comments first before sending out an updated series.

Thank you,
Pavel

On Wed, Nov 15, 2017 at 9:32 PM, Pavel Tatashin
<pasha.tatashin@...cle.com> wrote:
> changelog
> ---------
> 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()
>
> 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                 | 117 ++++++++++++++++++++++++++++------
>  arch/x86/xen/time.c                   |   7 +-
>  include/linux/timekeeping.h           |   3 +-
>  kernel/sched/clock.c                  |  10 ++-
>  kernel/time/timekeeping.c             |   8 ++-
>  11 files changed, 153 insertions(+), 30 deletions(-)
>
> --
> 2.15.0
>