Date:   Wed, 26 Apr 2017 20:13:08 +0200
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Paul E. McKenney" <paulmck@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: x86-tip tsc/tick gripage

On Wed, 2017-04-26 at 14:30 +0200, Mike Galbraith wrote:
> On Wed, 2017-04-26 at 13:39 +0200, Mike Galbraith wrote:
> > On Wed, 2017-04-26 at 12:26 +0200, Peter Zijlstra wrote:
> > > On Wed, Apr 26, 2017 at 10:57:42AM +0200, Mike Galbraith wrote:
> > > 
> > > > Both still lose their TSC.
> > > > 
> > > > [   11.982468] tsc: Refined TSC clocksource calibration: 2260.999 MHz
> > > > [   11.994275] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x20974a4d8bb, max_idle_ns: 440795246623 ns
> > > > [   13.064172] clocksource: Switched to clocksource tsc
> > > > [  240.247851] clocksource: timekeeping watchdog on CPU23: Marking clocksource 'tsc' as unstable because the skew is too large:
> > > > [  240.462501] clocksource:                       'tsc' cs_now: 108fe5be09f cs_last: b90a6a0676 mask: ffffffffffffffff
> > > > [  240.675057] tsc: Marking TSC unstable due to clocksource watchdog
> > > 
> > > 
> > > And they didn't use to? We don't typically write to TSC or TSC_ADJUST
> > > and thus would not cause such behaviour.
> > 
> > Nope.
> 
> DL980 seems perfectly happy with master.today.. so off we go.

ec2206b91d430da57c856869b5a37dc1e569e80d is the first bad commit
commit ec2206b91d430da57c856869b5a37dc1e569e80d
Author: Anna-Maria Gleixner <anna-maria@...utronix.de>
Date:   Mon Mar 20 10:34:20 2017 +0100

    timer: Implement the hierarchical pull model
    
    Placing timers at enqueue time on a target CPU based on dubious heuristics
    does not make any sense:
    
     1) Most timer wheel timers are canceled or rearmed before they expire.
    
     2) The heuristics to predict which CPU will be busy when the timer expires
        are wrong by definition.
    
    So we waste precious cycles to place timers at enqueue time.
    
    The proper solution to this problem is to always queue the timers on the
    local CPU and allow the non pinned timers to be pulled onto a busy CPU at
    expiry time.
    
    To achieve this the timer storage has been split into local pinned and
    global timers. Local pinned timers are always expired on the CPU on which
    they have been queued. Global timers can be expired on any CPU.
    
    As long as a CPU is busy it expires both local and global timers. When a
    CPU goes idle it arms for the first expiring local timer. If the first
    expiring pinned (local) timer is before the first expiring movable timer,
    then no action is required because the CPU will wake up before the first
    movable timer expires. If the first expiring movable timer is before the
    first expiring pinned (local) timer, then this timer is queued into a idle
    timerqueue and eventually expired by some other active CPU.
    
    To avoid global locking the timerqueues are implemented as a hierarchy. The
    lowest level of the hierarchy holds the CPUs. The CPUs are associated to
    groups of 8, which are seperated per node. If more than one CPU group
    exist, then a second level in the hierarchy collects the groups. Depending
    on the size of the system more than 2 levels are required. Each group has a
    "migrator" which checks the timerqueue during the tick for remote expirable
    timers.
    
    If the last CPU in a group goes idle it reports the first expiring event in
    the group up to the next group(s) in the hierarchy. If the last CPU goes
    idle it arms its timer for the first system wide expiring timer to ensure
    that no timer event is missed.
    
    Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
    Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

:040000 040000 76086a473919931466dfeea76a17566e2bb15130 5432a1bbc5ace9796e70e91447c6f26eb9eb51be M	include
:040000 040000 102292e74099b7c3e0b2125a4deef728267b4d9d 24385b3c68140fbb3362f32753f296d127e22097 M	kernel

git bisect start
# good: [ea839b41744dffe5c77b8d9842c9bb7073460901] Merge tag 'arc-4.11-final' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc
git bisect good ea839b41744dffe5c77b8d9842c9bb7073460901
# bad: [d02c59825bbfd2726430f410321f9d0bfc9d1ef4] Merge branch 'WIP.x86/fpu'
git bisect bad d02c59825bbfd2726430f410321f9d0bfc9d1ef4
# good: [1212249de8142df8c64c4165d1dee8ed4c3d766c] Merge branch 'perf/core'
git bisect good 1212249de8142df8c64c4165d1dee8ed4c3d766c
# good: [28a68c6ee0837004c87845a09717a99b4e96f7d4] Merge branch 'x86-mm-for-xen'
git bisect good 28a68c6ee0837004c87845a09717a99b4e96f7d4
# good: [7fd018291abbc076dc8073d48bba9614ca67b818] Merge branch 'x86/cleanups'
git bisect good 7fd018291abbc076dc8073d48bba9614ca67b818
# good: [6f029d98bc76cf9aa21e73e4beba9014e7e3adbb] Merge branch 'x86/platform'
git bisect good 6f029d98bc76cf9aa21e73e4beba9014e7e3adbb
# bad: [4691eff5d6475014b4c04481b03aff89f5ec87c1] Merge branch 'WIP.timers'
git bisect bad 4691eff5d6475014b4c04481b03aff89f5ec87c1
# good: [0605ab6fd5aa0c78133fc6611fa5e4f17e46c396] sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming
git bisect good 0605ab6fd5aa0c78133fc6611fa5e4f17e46c396
# bad: [1e1c48e6befca01abb2ed224a76fbe0ea8c73e30] timer: Always queue timers on the local CPU
git bisect bad 1e1c48e6befca01abb2ed224a76fbe0ea8c73e30
# good: [c82a8b6b216e6910f36a94939de7e8793b25feaa] timer: Retrieve next expiry of pinned/non-pinned timers seperately
git bisect good c82a8b6b216e6910f36a94939de7e8793b25feaa
# good: [e2e1214438bb25ec4e37b8aedb3d3e502535b09b] tick/sched: Split out jiffies update helper function
git bisect good e2e1214438bb25ec4e37b8aedb3d3e502535b09b
# bad: [270c4e558cc26a0d89e89dda46c35ac39457a896] timer_migration: Add tracepoints
git bisect bad 270c4e558cc26a0d89e89dda46c35ac39457a896
# bad: [ec2206b91d430da57c856869b5a37dc1e569e80d] timer: Implement the hierarchical pull model
git bisect bad ec2206b91d430da57c856869b5a37dc1e569e80d

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