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timekeeping: Use proper timekeeper for debug code

PATCH In review Stafford Horne 2 participants 7 messages Jun 28, 2017 – Jul 6, 2017 Timekeeping, clocksource core, NTP, alarmtimer

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Stafford Horne

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#0 lore raw

PATCH 1/1 timekeeping: Use proper timekeeper for debug code

When CONFIG_DEBUG_TIMEKEEPING is enabled the timekeeping_check_update() function will update status like last_warning and underflow_seen on the timekeeper.

If there are issues found this state is used to rate limit the warnings that get printed.

This rate limiting doesn't really really work if stored in real_tk as the shadow timekeeper is overwritten onto real_tk at the end of every update_wall_time() call, resetting last_warning and other statuses.

Fix rate limiting by using the shadow_timekeeper for timekeeping_check_update().

Fixes commit 57d05a93ada7 ("time: Rework debugging variables so they aren't global")
Signed-off-by Stafford Horne <[email protected]>
---
 kernel/time/timekeeping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/time/timekeeping.c +1 -1
index 9652bc5..061088c 100644
@@ -2039,7 +2039,7 @@ void update_wall_time(void)
 		goto out;
 
 	/* Do some additional sanity checking */
-	timekeeping_check_update(real_tk, offset);
+	timekeeping_check_update(tk, offset);
 
 	/*
 	 * With NO_HZ we may have to accumulate many cycle_intervals
Signature · 1 line
2.9.4
#1 lore raw
Quoted 11 lines · Stafford Horne

When CONFIG_DEBUG_TIMEKEEPING is enabled the timekeeping_check_update() function will update status like last_warning and underflow_seen on the timekeeper.

If there are issues found this state is used to rate limit the warnings that get printed.

This rate limiting doesn't really really work if stored in real_tk as the shadow timekeeper is overwritten onto real_tk at the end of every update_wall_time() call, resetting last_warning and other statuses.

Quoted 5 lines

Fix rate limiting by using the shadow_timekeeper for timekeeping_check_update().

Fixes commit 57d05a93ada7 ("time: Rework debugging variables so they aren't global")
Signed-off-by Stafford Horne <[email protected]>

Interesting! Thanks for submitting this! Out of curiosity, can you also talk about the underlying issue that made you come across this issue?

thanks
-john

author
#2 lore raw
Quoted 15 lines · John Stultz
Quoted 14 lines · Stafford Horne

When CONFIG_DEBUG_TIMEKEEPING is enabled the timekeeping_check_update() function will update status like last_warning and underflow_seen on the timekeeper.

If there are issues found this state is used to rate limit the warnings that get printed.

This rate limiting doesn't really really work if stored in real_tk as the shadow timekeeper is overwritten onto real_tk at the end of every update_wall_time() call, resetting last_warning and other statuses.

Fix rate limiting by using the shadow_timekeeper for timekeeping_check_update().

Quoted 6 lines
Quoted 2 lines
Fixes commit 57d05a93ada7 ("time: Rework debugging variables so they aren't global")
Signed-off-by Stafford Horne <[email protected]>

Interesting! Thanks for submitting this! Out of curiosity, can you also talk about the underlying issue that made you come across this issue?

I am working on OpenRISC SMP support. There was one issue where the per_cpu internal timers (used as clocksource) were not in sync, this pointed it out.

There is another issue right now when switching from jiffies to the openrisc clocksource. Which is maybe ok because each have different starting points.

[    0.160000] clocksource: Switched to clocksource openrisc_timer
[    0.220000] INFO: timekeeping: Cycle offset (4294173293) is larger than the 'openrisc_timer' clock's 50% safety margin (2147483647)
[    0.220000]       timekeeping: Your kernel is still fine, but is feeling a bit nervous

Let me know if you want me to add this to the commit message in a v2.

-Stafford

author
#3 lore raw
In reply to John Stultz

Hi tglx,

Sorry, to bother you, I thought maybe this you missed this one? Let me know if you want a resend.

-Stafford

Quoted 24 lines · John Stultz
Quoted 11 lines · Stafford Horne

When CONFIG_DEBUG_TIMEKEEPING is enabled the timekeeping_check_update() function will update status like last_warning and underflow_seen on the timekeeper.

If there are issues found this state is used to rate limit the warnings that get printed.

This rate limiting doesn't really really work if stored in real_tk as the shadow timekeeper is overwritten onto real_tk at the end of every update_wall_time() call, resetting last_warning and other statuses.

Quoted 5 lines

Fix rate limiting by using the shadow_timekeeper for timekeeping_check_update().

Fixes commit 57d05a93ada7 ("time: Rework debugging variables so they aren't global")
Signed-off-by Stafford Horne <[email protected]>

Interesting! Thanks for submitting this! Out of curiosity, can you also talk about the underlying issue that made you come across this issue?

thanks
-john

#4 lore raw
Quoted 4 lines · Stafford Horne

Hi tglx,

Sorry, to bother you, I thought maybe this you missed this one? Let me know if you want a resend.

No. Sorry, I've already got this queued. Apologies for not sending notice.

thanks
-john

author
#5 lore raw
Quoted 7 lines · John Stultz
Quoted 4 lines · Stafford Horne

Hi tglx,

Sorry, to bother you, I thought maybe this you missed this one? Let me know if you want a resend.

No. Sorry, I've already got this queued. Apologies for not sending notice.

Oh, no problem, I thought maybe it would go to tip as I didnt see your queue.

Thanks you
-Stafford

#6 lore raw
Quoted 11 lines · Stafford Horne
Quoted 7 lines · John Stultz
Quoted 4 lines · Stafford Horne

Hi tglx,

Sorry, to bother you, I thought maybe this you missed this one? Let me know if you want a resend.

No. Sorry, I've already got this queued. Apologies for not sending notice.

Oh, no problem, I thought maybe it would go to tip as I didnt see your queue.

I've not yet pushed it out, but the initial testing looked ok.

thanks
-john