This is a note to let you know that I've just added the patch titled
sched/cputime: Fix steal_account_process_tick() to always return jiffies
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-cputime-fix-steal_account_process_tick-to-always-return-jiffies.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f9c904b7613b8b4c85b10cd6b33ad41b2843fa9d Mon Sep 17 00:00:00 2001
From: Chris Friesen <cbf123@xxxxxxxxxxxxx>
Date: Sat, 5 Mar 2016 23:18:48 -0600
Subject: sched/cputime: Fix steal_account_process_tick() to always return jiffies
From: Chris Friesen <cbf123@xxxxxxxxxxxxx>
commit f9c904b7613b8b4c85b10cd6b33ad41b2843fa9d upstream.
The callers of steal_account_process_tick() expect it to return
whether a jiffy should be considered stolen or not.
Currently the return value of steal_account_process_tick() is in
units of cputime, which vary between either jiffies or nsecs
depending on CONFIG_VIRT_CPU_ACCOUNTING_GEN.
If cputime has nsecs granularity and there is a tiny amount of
stolen time (a few nsecs, say) then we will consider the entire
tick stolen and will not account the tick on user/system/idle,
causing /proc/stats to show invalid data.
The fix is to change steal_account_process_tick() to accumulate
the stolen time and only account it once it's worth a jiffy.
(Thanks to Frederic Weisbecker for suggestions to fix a bug in my
first version of the patch.)
Signed-off-by: Chris Friesen <chris.friesen@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/56DBBDB8.40305@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/cputime.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -259,21 +259,21 @@ static __always_inline bool steal_accoun
#ifdef CONFIG_PARAVIRT
if (static_key_false(¶virt_steal_enabled)) {
u64 steal;
- cputime_t steal_ct;
+ unsigned long steal_jiffies;
steal = paravirt_steal_clock(smp_processor_id());
steal -= this_rq()->prev_steal_time;
/*
- * cputime_t may be less precise than nsecs (eg: if it's
- * based on jiffies). Lets cast the result to cputime
+ * steal is in nsecs but our caller is expecting steal
+ * time in jiffies. Lets cast the result to jiffies
* granularity and account the rest on the next rounds.
*/
- steal_ct = nsecs_to_cputime(steal);
- this_rq()->prev_steal_time += cputime_to_nsecs(steal_ct);
+ steal_jiffies = nsecs_to_jiffies(steal);
+ this_rq()->prev_steal_time += jiffies_to_nsecs(steal_jiffies);
- account_steal_time(steal_ct);
- return steal_ct;
+ account_steal_time(jiffies_to_cputime(steal_jiffies));
+ return steal_jiffies;
}
#endif
return false;
Patches currently in stable-queue which might be from cbf123@xxxxxxxxxxxxx are
queue-4.4/sched-cputime-fix-steal_account_process_tick-to-always-return-jiffies.patch
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