Hi Greg,
This series fixes issues we've seen with softirq time accounting in 4.9:
- when ksoftirqd is running at 100% on a CPU, none of the values
reported by /proc/stat for that CPU will change, sometimes for
dozens of seconds,
- large deviations in the total number of ticks accumulated over a
fixed time for a CPU, probably because of the first issue hitting
for shorter periods.
We found out that something pretty similar had been reported 9 months
ago, see the reference link below. In that discussion, Rabin Vincent had
made a 4.9 specific patch which fixes our first issue, but we were still
seeing some deviation from the total number of ticks (up to 1.7% from
expected, where we had only 0.2% on older kernels), and you had also
asked for a direct backport from the mainline series, if possible.
As mentioned in that thread, a lot of changes (probably 50+) went into
4.11 to remove cputime, but we could get something working with only the
4 attached patches to fix these two issues. Three of these patches apply
without change, and the second one in the series ("sched/cputime:
Convert kcpustat to nsecs") needed a minor change as a cast had been
added in 527b0a76f41d ("sched/cpuacct: Avoid %lld seq_printf warning")
to fix a build warning on s390. I guess we could also include that patch
in this series, let me know if this is the preferred way to handle this.
We ran our tests on 3.18, 4.4 and 4.9 and confirmed that only 4.9 would
need this series, and that this series indeed restores the behavior we
were seeing on those older kernels.
Thanks!
Reference: http://lkml.kernel.org/r/%3C1513159876-5125-1-git-send-email-rabin.vincent@xxxxxxxx
Frederic Weisbecker (4):
time: Introduce jiffies64_to_nsecs()
sched/cputime: Convert kcpustat to nsecs
sched/cputime: Increment kcpustat directly on irqtime account
sched/cputime: Fix ksoftirqd cputime accounting regression
arch/s390/appldata/appldata_os.c | 16 +++----
drivers/cpufreq/cpufreq.c | 6 +--
drivers/cpufreq/cpufreq_governor.c | 2 +-
drivers/cpufreq/cpufreq_stats.c | 1 -
drivers/macintosh/rack-meter.c | 2 +-
fs/proc/stat.c | 68 +++++++++++++--------------
fs/proc/uptime.c | 7 +--
include/linux/jiffies.h | 2 +
kernel/sched/cpuacct.c | 2 +-
kernel/sched/cputime.c | 75 +++++++++++++-----------------
kernel/sched/sched.h | 12 +++--
kernel/time/time.c | 10 ++++
kernel/time/timeconst.bc | 6 +++
13 files changed, 109 insertions(+), 100 deletions(-)
--
2.18.0
