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authorChris Friesen <cbf123@mail.usask.ca>2016-03-05 23:18:48 -0600
committerIngo Molnar <mingo@kernel.org>2016-03-08 12:24:56 +0100
commitf9c904b7613b8b4c85b10cd6b33ad41b2843fa9d (patch)
tree96f16153b74572cf26a98c8028ffe315f5cbafe7 /kernel
parent72f9f3fdc928dc3ecd223e801b32d930b662b6ed (diff)
downloadlinux-f9c904b7613b8b4c85b10cd6b33ad41b2843fa9d.tar.bz2
sched/cputime: Fix steal_account_process_tick() to always return jiffies
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@windriver.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: <stable@vger.kernel.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/56DBBDB8.40305@mail.usask.ca Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/cputime.c14
1 files changed, 7 insertions, 7 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 01d9898bc9a2..75f98c5498d5 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -262,21 +262,21 @@ static __always_inline bool steal_account_process_tick(void)
#ifdef CONFIG_PARAVIRT
if (static_key_false(&paravirt_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;