The patch titled
Subject: nohz: fix idle ticks in cpu summary line of /proc/stat
has been added to the -mm tree. Its filename is
nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat.patch
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From: Michal Hocko <mhocko@xxxxxxx>
Subject: nohz: fix idle ticks in cpu summary line of /proc/stat
Commit 09a1d34f8535ecf9 ("nohz: Make idle/iowait counter update
conditional") introduced a bug in regard to cpu hotplug. The effect is
that the number of idle ticks in the cpu summary line in /proc/stat is
still counting ticks for offline cpus.
Reproduction is easy, just start a workload that keeps all cpus busy,
switch off one or more cpus and then watch the idle field in top. On a
dual-core with one cpu 100% busy and one offline cpu you will get
something like this:
%Cpu(s): 48.7 us, 1.3 sy, 0.0 ni, 50.0 id, 0.0 wa, 0.0 hi, 0.0 si,
%0.0 st
The problem is that an offline cpu still has ts->idle_active == 1. To fix
this we should make sure that the cpu is online when calling
get_cpu_idle_time_us and get_cpu_iowait_time_us.
[srivatsa.bhat@xxxxxxxxxxxxxxxxxx: rebased to current mainline]
Reported-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/stat.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff -puN fs/proc/stat.c~nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat fs/proc/stat.c
--- a/fs/proc/stat.c~nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat
+++ a/fs/proc/stat.c
@@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int c
static u64 get_idle_time(int cpu)
{
- u64 idle, idle_time = get_cpu_idle_time_us(cpu, NULL);
+ u64 idle, idle_time = -1ULL;
+
+ if (cpu_online(cpu))
+ idle_time = get_cpu_idle_time_us(cpu, NULL);
if (idle_time == -1ULL)
- /* !NO_HZ so we can rely on cpustat.idle */
+ /* !NO_HZ or cpu offline so we can rely on cpustat.idle */
idle = kcpustat_cpu(cpu).cpustat[CPUTIME_IDLE];
else
idle = usecs_to_cputime64(idle_time);
@@ -58,10 +61,13 @@ static u64 get_idle_time(int cpu)
static u64 get_iowait_time(int cpu)
{
- u64 iowait, iowait_time = get_cpu_iowait_time_us(cpu, NULL);
+ u64 iowait, iowait_time = -1ULL;
+
+ if (cpu_online(cpu))
+ iowait_time = get_cpu_iowait_time_us(cpu, NULL);
if (iowait_time == -1ULL)
- /* !NO_HZ so we can rely on cpustat.iowait */
+ /* !NO_HZ or cpu offline so we can rely on cpustat.iowait */
iowait = kcpustat_cpu(cpu).cpustat[CPUTIME_IOWAIT];
else
iowait = usecs_to_cputime64(iowait_time);
_
Patches currently in -mm which might be from mhocko@xxxxxxx are
origin.patch
nohz-fix-idle-ticks-in-cpu-summary-line-of-proc-stat.patch
mm-memblock-reduce-overhead-in-binary-search.patch
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