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SubjectRe: 2.6.25-rc5-git6: Reported regressions from 2.6.24
Gabriel C wrote:
> Thomas Gleixner wrote:
>> On Mon, 17 Mar 2008, Gabriel C wrote:
>>>> Subject : Clocksource tsc is always unstable with 2.6.25-* kernels and CONFIG_NO_HZ=y on my box
>>>> Submitter : Gabriel C <>
>>>> Date : 2008-02-24 01:31 (22 days old)
>>>> References :
>>>> Handled-By : Thomas Gleixner <>
>>> Thomas do you want me to bisect ?
>> That'd be great.
> Ok I'll start doing that later on today.

I managed to bisect 'one of the bugs' down , I got some problems and used skip once because a revision didn't compiled ,
but it seems bisect got the right commit still. Sadly it seems there are 2 different bugs.

Also before I've started the bisect I've tested linux-next to be sure the bug(s) still exists and while rc1 got that already
I've started to bisect 2.6.24 -> 2.6.25-rc1.

cat .git/refs/bisect/bad

git show 1ada5cba6a0318f90e45b38557e7b5206a9cba38
commit 1ada5cba6a0318f90e45b38557e7b5206a9cba38
Author: Andi Kleen <>
Date: Wed Jan 30 13:30:02 2008 +0100

clocksource: make clocksource watchdog cycle through online CPUs

This way it checks if the clocks are synchronized between CPUs too.
This might be able to detect slowly drifting TSCs which only
go wrong over longer time.

Signed-off-by: Andi Kleen <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Thomas Gleixner <>

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index cabfa19..edd5ef8 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -142,8 +142,13 @@ static void clocksource_watchdog(unsigned long data)

if (!list_empty(&watchdog_list)) {
- __mod_timer(&watchdog_timer,
- watchdog_timer.expires + WATCHDOG_INTERVAL);
+ /* Cycle through CPUs to check if the CPUs stay synchronized to
+ * each other. */
+ int next_cpu = next_cpu(raw_smp_processor_id(), cpu_online_map);
+ if (next_cpu >= NR_CPUS)
+ next_cpu = first_cpu(cpu_online_map);
+ watchdog_timer.expires += WATCHDOG_INTERVAL;
+ add_timer_on(&watchdog_timer, next_cpu);
@@ -165,7 +170,7 @@ static void clocksource_check_watchdog(struct clocksource *cs)
if (!started && watchdog) {
watchdog_last = watchdog->read();
watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
- add_timer(&watchdog_timer);
+ add_timer_on(&watchdog_timer, first_cpu(cpu_online_map));
} else {
@@ -186,7 +191,8 @@ static void clocksource_check_watchdog(struct clocksource *cs)
watchdog_last = watchdog->read();
watchdog_timer.expires =
- add_timer(&watchdog_timer);
+ add_timer_on(&watchdog_timer,
+ first_cpu(cpu_online_map));

git bisect log
git-bisect start
# bad: [19af35546de68c872dcb687613e0902a602cb20e] Linux 2.6.25-rc1
git-bisect bad 19af35546de68c872dcb687613e0902a602cb20e
# good: [49914084e797530d9baaf51df9eda77babc98fa8] Linux 2.6.24
git-bisect good 49914084e797530d9baaf51df9eda77babc98fa8
# bad: [d2e626f45cc450c00f5f98a89b8b4c4ac3c9bf5f] x86: add PAGE_KERNEL_EXEC_NOCACHE
git-bisect bad d2e626f45cc450c00f5f98a89b8b4c4ac3c9bf5f
# good: [fb46990dba94866462e90623e183d02ec591cf8f] [NETFILTER]: nf_queue: remove unnecessary hook existance check
git-bisect good fb46990dba94866462e90623e183d02ec591cf8f
# good: [936722922f6d2366378de606a40c14f96915474d] [IPV4] fib_trie: compute size when needed
git-bisect good 936722922f6d2366378de606a40c14f96915474d
# bad: [ff14c6164bd532a6dc9025c07d3b562f839f00a9] x86: x86-64 ia32 ptrace pt_regs cleanup
git-bisect bad ff14c6164bd532a6dc9025c07d3b562f839f00a9
# good: [c087567d3ffb2c7c61e091982e6ca45478394f1a] SUNRPC: Remove the obsolete RPC_WAITQ macro
git-bisect good c087567d3ffb2c7c61e091982e6ca45478394f1a
# bad: [af7a78e9258ffcca681e080cbc857f854869144f] x86: move mce related declarations
git-bisect bad af7a78e9258ffcca681e080cbc857f854869144f
# good: [34f5b4662bf4b54f22b32ce76ce70eccd7ebc68a] SUNRPC: Don't bother changing the sigmask for asynchronous RPC calls
git-bisect good 34f5b4662bf4b54f22b32ce76ce70eccd7ebc68a
# bad: [83bd01024b1fdfc41d9b758e5669e80fca72df66] x86: protect against sigaltstack wraparound
git-bisect bad 83bd01024b1fdfc41d9b758e5669e80fca72df66
# good: [efd9ac8630e89b9ee7ce64008bd7783952374f37] time: fold __get_realtime_clock_ts() into getnstimeofday()
git-bisect good efd9ac8630e89b9ee7ce64008bd7783952374f37
# bad: [37a47db8d7f0f38dac5acf5a13abbc8f401707fa] x86: assign IRQs to HPET timers, fix
git-bisect bad 37a47db8d7f0f38dac5acf5a13abbc8f401707fa
# skip: [316da3b3fc8efa9a5d2c99e0d449f01ff38c6aba] x86: restrict PIT clocksource usage
git-bisect skip 316da3b3fc8efa9a5d2c99e0d449f01ff38c6aba
# bad: [4713e22ce81eb8b3353e16435362eb3d0ec95640] clocksource: add unregister function to disable unusable clocksources
git-bisect bad 4713e22ce81eb8b3353e16435362eb3d0ec95640
# bad: [1ada5cba6a0318f90e45b38557e7b5206a9cba38] clocksource: make clocksource watchdog cycle through online CPUs
git-bisect bad 1ada5cba6a0318f90e45b38557e7b5206a9cba38
# good: [1077f5a917b7c630231037826b344b2f7f5b903f] clocksource.c: use init_timer_deferrable for clocksource_watchdog
git-bisect good 1077f5a917b7c630231037826b344b2f7f5b903f

Also the broken revision died with that :

arch/x86/kernel/i8253.c: In function 'init_pit_clocksource':
arch/x86/kernel/i8253.c:207: error: implicit declaration of function 'is_hpet_enabled'
make[1]: *** [arch/x86/kernel/i8253.o] Error 1
make: *** [arch/x86/kernel] Error 2

If you tell me on how to fix that I'll restart the bisect from there , just in case ..

Also reverting the commit from 2.6.25-rc1 fixes the 'Tsc being unstable thing' but it does not fix the hang
when I boot with clocksource=acpi_pm so that seems to be introduced in a different commit.

I will try to bisect this hang also , most probably on weekend.

Also I reverted that commit from git head and an kernel compiles right now, I'll let you know in a bit if that worked out.

Please let me know if you need more informations.

Best Regards,


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