nohz: add missing handling of clocksource watchdog
PATCH 1/1 nohz: add missing handling of clocksource watchdog
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.
[ IDE was unlucky to be initialized at the same time that clocksource watchdog triggers and was blamed for the issue. ]
Cc: Sergei Shtylyov <[email protected]>Cc: Lars Winterfeld <[email protected]>Signed-off-by: Bartlomiej Zolnierkiewicz <[email protected]>--- kernel/time/tick-sched.c | 2 ++ 1 file changed, 2 insertions(+)
Index: b/kernel/time/tick-sched.c===================================================================--- a/kernel/time/tick-sched.c+++ b/kernel/time/tick-sched.c@@ -21,6 +21,7 @@ #include <linux/sched.h> #include <linux/tick.h> #include <linux/module.h>+#include <linux/clocksource.h> #include <asm/irq_regs.h> @@ -153,6 +154,7 @@ void tick_nohz_update_jiffies(void) local_irq_restore(flags); touch_softlockup_watchdog();+ clocksource_touch_watchdog(); } static void tick_nohz_stop_idle(int cpu) ÿôèº{.nÇ+‰·Ÿ®‰†+%ŠËÿ±éݶ¥Šwÿº{.nÇ+‰·¥Š{±þG«�éÿŠ{ayº ʇڙë,j¢f£¢·hš�ï�êÿ‘êçz_è®(階ŠÝ¢j"�ú¶m§ÿÿ¾«þG«�éÿ¢¸?™¨èÚ&£ø§~�á¶iO•æ¬z·švØ^¶m§ÿÿà ÿ¶ìÿ¢¸?–I¥
Hello.
Quoted 7 lines · R. J. Wysocki
Quoted 2 lines · Bartlomiej Zolnierkiewicz
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.
Where can I find the description of the problem?
Kernel.org bug #10216 (it's not about this issue though).
Quoted 6 lines
Rafael
Quoted 3 lines
[ IDE was unlucky to be initialized at the same time that
clocksource watchdog triggers and was blamed for the issue. ]
I think it might well have been blamed correctly -- the clocksource
watchdog timer gets run every half second.
MBR, Sergei
Quoted 2 lines · Bartlomiej Zolnierkiewicz
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.
Where can I find the description of the problem?
Rafael
Quoted 31 lines
[ IDE was unlucky to be initialized at the same time that
clocksource watchdog triggers and was blamed for the issue. ]Cc Sergei Shtylyov <[email protected]>Cc Lars Winterfeld <[email protected]>Signed-off-by Bartlomiej Zolnierkiewicz <[email protected]>--- kernel/time/tick-sched.c | 2 ++ 1 file changed, 2 insertions(+)Index:
b/kernel/time/tick-sched.c
===================================================================kernel/time/tick-sched.c +2
-0@@ -21,6 +21,7 @@#include <linux/sched.h> #include <linux/tick.h> #include <linux/module.h> +#include <linux/clocksource.h> #include <asm/irq_regs.h> @@ -153,6 +154,7 @@ void tick_nohz_update_jiffies(void)local_irq_restore (flags);touch_softlockup_watchdog (); +clocksource_touch_watchdog (); }static void tick_nohz_stop_idle (int cpu)
Signature · 10 lines
Rafael J. Wysocki, Ph.D. Institute of Theoretical Physics Faculty of Physics of Warsaw University ul. Hoza 69, 00-681 Warsaw [tel: +48 22 55 32 263] [mob: +48 60 50 53 693] ---------------------------- One should not increase, beyond what is necessary, the number of entities required to explain anything. -- William of Ockham
On Monday 08 December 2008, Sergei Shtylyov wrote:> Hello.> > R. J. Wysocki wrote:> > On Monday, 8 of December 2008, Bartlomiej Zolnierkiewicz wrote:> > > >> Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.> >> > >> > Where can I find the description of the problem?> > > > Kernel.org bug #10216 (it's not about this issue though).
Looking back at bug #10216 the patch is unlikely to help Lars' systemsince it doesn't use nohz and there are also warnings about unsyncedTSCs (I just don't know why not for 2.6.27-rc kernels)... > > Rafael> >> > > >> [ IDE was unlucky to be initialized at the same time that> >> clocksource watchdog triggers and was blamed for the issue. ]> >> > > I think it might well have been blamed correctly -- the clocksource > watchdog timer gets run every half second.
AFAICS this is a special one for measuring stability of the clocksourceonly -- by comparing the value returned by a given clocksource with thereference clocksource. Normal drivers have no bussiness there... Anyway I forgot to add that it fixes the issue for me under QEMU (on mylaptop TSC is unstable due to halts in idle) and it could be as well QEMU'soddity (although it looks like a legit kernel problem). v2 of the patchbelow (updated patch description).
From: Bartlomiej Zolnierkiewicz <[email protected]>Subject: [PATCH v2] nohz: add missing handling of clocksource watchdog
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problemunder QEMU.
Cc: Sergei Shtylyov <[email protected]>Cc: Lars Winterfeld <[email protected]>Signed-off-by: Bartlomiej Zolnierkiewicz <[email protected]>--- kernel/time/tick-sched.c | 2 ++ 1 file changed, 2 insertions(+)
Index: b/kernel/time/tick-sched.c===================================================================--- a/kernel/time/tick-sched.c+++ b/kernel/time/tick-sched.c@@ -21,6 +21,7 @@ #include <linux/sched.h> #include <linux/tick.h> #include <linux/module.h>+#include <linux/clocksource.h> #include <asm/irq_regs.h> @@ -153,6 +154,7 @@ void tick_nohz_update_jiffies(void) local_irq_restore(flags); touch_softlockup_watchdog();+ clocksource_touch_watchdog(); } static void tick_nohz_stop_idle(int cpu) ÿôèº{.nÇ+‰·Ÿ®‰†+%ŠËÿ±éݶ¥Šwÿº{.nÇ+‰·¥Š{±þG«�éÿŠ{ayº ʇڙë,j¢f£¢·hš�ï�êÿ‘êçz_è®(階ŠÝ¢j"�ú¶m§ÿÿ¾«þG«�éÿ¢¸?™¨èÚ&£ø§~�á¶iO•æ¬z·švØ^¶m§ÿÿà ÿ¶ìÿ¢¸?–I¥
Thomas Gleixner
NAKQuoted 63 lines · Bartlomiej Zolnierkiewicz
Quoted 5 lines · Sergei Shtylyov
Hello.
Quoted 2 lines · R. J. Wysocki
On Monday, 8 of December 2008, Bartlomiej Zolnierkiewicz wrote:
Quoted 7 lines
Quoted 5 lines
Quoted 2 lines
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.
Where can I find the description of the problem?
Kernel.org bug #10216 (it's not about this issue though).
Looking back at bug #10216 the patch is unlikely to help Lars' system since it doesn't use nohz and there are also warnings about unsynced TSCs (I just don't know why not for 2.6.27-rc kernels)...
Quoted 9 lines
Quoted 6 lines
Rafael
Quoted 3 lines
[ IDE was unlucky to be initialized at the same time that
clocksource watchdog triggers and was blamed for the issue. ]I think it might well have been blamed correctly -- the clocksource
watchdog timer gets run every half second.AFAICS this is a special one for measuring stability of the clocksource only -- by comparing the value returned by a given clocksource with the reference clocksource. Normal drivers have no bussiness there...
Anyway I forgot to add that it fixes the issue for me under QEMU (on my laptop TSC is unstable due to halts in idle) and it could be as well QEMU's oddity (although it looks like a legit kernel problem). v2 of the patch below (updated patch description).
From: Bartlomiej Zolnierkiewicz <[email protected]>
Subject: [PATCH v2] nohz: add missing handling of clocksource watchdogFixes "Clocksource tsc unstable (delta = -974982308 ns)" problem under QEMU.
Cc Sergei Shtylyov <[email protected]>Cc Lars Winterfeld <[email protected]>Signed-off-by Bartlomiej Zolnierkiewicz <[email protected]>--- kernel/time/tick-sched.c | 2 ++ 1 file changed, 2 insertions(+)Index:
b/kernel/time/tick-sched.c
===================================================================kernel/time/tick-sched.c +1
-0@@ -21,6 +21,7 @@#include <linux/sched.h> #include <linux/tick.h> #include <linux/module.h> +#include <linux/clocksource.h> #include <asm/irq_regs.h>
kernel/time/tick-sched.c void tick_nohz_update_jiffies(void) · line 157
Quoted 4 lines
kernel/time/tick-sched.c +1
-0@@ -153,6 +154,7 @@ void tick_nohz_update_jiffies(void)local_irq_restore (flags);touch_softlockup_watchdog (); +clocksource_touch_watchdog ();
NAK.
If this happens then the watchdog logic did not manage to schedule the watchdog timer in time. This patch just papers over the real problem.
We do not fix QEMU problems in the kernel, as we would miss real hardware wreckage that way.
Thanks,
tglx
Quoted 72 lines · Thomas Gleixner
Quoted 63 lines · Bartlomiej Zolnierkiewicz
Quoted 5 lines · Sergei Shtylyov
Hello.
Quoted 2 lines · R. J. Wysocki
On Monday, 8 of December 2008, Bartlomiej Zolnierkiewicz wrote:
Quoted 7 lines
Quoted 5 lines
Quoted 2 lines
Fixes "Clocksource tsc unstable (delta = -974982308 ns)" problem.
Where can I find the description of the problem?
Kernel.org bug #10216 (it's not about this issue though).
Looking back at bug #10216 the patch is unlikely to help Lars' system since it doesn't use nohz and there are also warnings about unsynced TSCs (I just don't know why not for 2.6.27-rc kernels)...
Quoted 9 lines
Quoted 6 lines
Rafael
Quoted 3 lines
[ IDE was unlucky to be initialized at the same time that
clocksource watchdog triggers and was blamed for the issue. ]I think it might well have been blamed correctly -- the clocksource
watchdog timer gets run every half second.AFAICS this is a special one for measuring stability of the clocksource only -- by comparing the value returned by a given clocksource with the reference clocksource. Normal drivers have no bussiness there...
Anyway I forgot to add that it fixes the issue for me under QEMU (on my laptop TSC is unstable due to halts in idle) and it could be as well QEMU's oddity (although it looks like a legit kernel problem). v2 of the patch below (updated patch description).
From: Bartlomiej Zolnierkiewicz <[email protected]>
Subject: [PATCH v2] nohz: add missing handling of clocksource watchdogFixes "Clocksource tsc unstable (delta = -974982308 ns)" problem under QEMU.
Cc Sergei Shtylyov <[email protected]>Cc Lars Winterfeld <[email protected]>Signed-off-by Bartlomiej Zolnierkiewicz <[email protected]>--- kernel/time/tick-sched.c | 2 ++ 1 file changed, 2 insertions(+)Index:
b/kernel/time/tick-sched.c
===================================================================kernel/time/tick-sched.c +1
-0@@ -21,6 +21,7 @@#include <linux/sched.h> #include <linux/tick.h> #include <linux/module.h> +#include <linux/clocksource.h> #include <asm/irq_regs.h> kernel/time/tick-sched.c void tick_nohz_update_jiffies(void) · line 157
Quoted 4 lines
kernel/time/tick-sched.c +1
-0@@ -153,6 +154,7 @@ void tick_nohz_update_jiffies(void)local_irq_restore (flags);touch_softlockup_watchdog (); +clocksource_touch_watchdog ();NAK.
Quoted 5 lines
If this happens then the watchdog logic did not manage to schedule the watchdog timer in time. This patch just papers over the real problem.
We do not fix QEMU problems in the kernel, as we would miss real hardware wreckage that way.
I know that and I'm not proposing it. However sometimes things that look like QEMU specific problems indicate the real deficiencies of the kernel.
I did more debugging and the reason for marking tsc clocksource as an unstable is that the reference clocksource (acpi_pm) itself is bad. The similar problems seem to also happen with the real hardware, i.e. please see:
http://lkml.indiana.edu/hypermail/linux/kernel/0802.3/0589.html
I cooked up a debug patch which uses timer interval as a reference for checking stability of the watchdog clocksource (I think it could be useful for debugging similar issues, it is not a generic solution since it doesn't handle the situation when both watchdog and watched clocksources are bad).
I'm also wondering whether it would be a good idea to modify our clocksource watchdog code to just always use timer interval as reference for checking clocksource stability. It will allow us to check all clocksources (including watchdog one) and should simplify the code a bit. I can make a patch for it if you think that this is good idea...
--- kernel/time/clocksource.c | 39 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 37 insertions(+), 2 deletions(-)
kernel/time/clocksource.c +37 -2
@@ -79,8 +79,9 @@ static unsigned long watchdog_resumed;/* * Interval: 0.5sec Threshold: 0.0625s */ -#define WATCHDOG_INTERVAL (HZ >> 1) -#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4) +#define WATCHDOG_INTERVAL (HZ >> 1) +#define WATCHDOG_INTERVAL_NSEC 500000000 +#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)static void clocksource_ratewd (struct clocksource *cs,int64_t delta) {
@@ -94,6 +95,34 @@ static void clocksource_ratewd(struct cllist_del (&cs->wd_list); } +static int watchdog_check (struct clocksource *wd, +int64_t wd_nsec,int64_t cs_nsec) +{ +int64_t delta; + +/* check if watchdog seems good */ + delta = wd_nsec -WATCHDOG_INTERVAL_NSEC ; +if (delta > -WATCHDOG_THRESHOLD && delta <WATCHDOG_THRESHOLD ) +return 0 ; + +/* check if clocksource seems bad */ + delta = cs_nsec -WATCHDOG_INTERVAL_NSEC ; +if (delta < -WATCHDOG_THRESHOLD || delta >WATCHDOG_THRESHOLD ) +return 0 ; + +printk (KERN_WARNING "Watchdog clocksource %s unstable (delta = " +"%lld ns)\n" , wd->name, wd_nsec -WATCHDOG_INTERVAL_NSEC ); + + wd->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES |CLOCK_SOURCE_WATCHDOG ); +clocksource_change_rating (wd,0 ); + +/* disable watchdog */ + watchdog =NULL ; + +/* don't add next timer */ +return 1 ; +} +static void clocksource_watchdog (unsigned long data) {struct clocksource *cs, *tmp;
@@ -135,6 +164,11 @@ static void clocksource_watchdog(unsigne }else { cs_nsec =cyc2ns (cs, (csnow - cs->wd_last) & cs->mask); cs->wd_last = csnow; + +/* Check reference clock stability first. */ +if (watchdog_check (watchdog, wd_nsec, cs_nsec)) + goto out_unlock; +/* Check the delta. Might remove from the list ! */ clocksource_ratewd (cs, cs_nsec - wd_nsec); }
@@ -152,6 +186,7 @@ static void clocksource_watchdog(unsigne watchdog_timer.expires +=WATCHDOG_INTERVAL ;add_timer_on (&watchdog_timer, next_cpu); } +out_unlock:spin_unlock (&watchdog_lock); }static void clocksource_resume_watchdog (void )