* [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat
@ 2012-09-10 11:13 Srivatsa S. Bhat
2012-09-25 18:50 ` Srivatsa S. Bhat
0 siblings, 1 reply; 3+ messages in thread
From: Srivatsa S. Bhat @ 2012-09-10 11:13 UTC (permalink / raw)
To: tglx, mhocko; +Cc: schwidefsky, deepthi, linux-kernel, srivatsa.bhat
From: Michal Hocko <mhocko@suse.cz>
Git 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.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
[srivatsa.bhat@linux.vnet.ibm.com: Rebased to current mainline]
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---
Hi Thomas,
This is a resend of the patch posted by Michal at [1]. Martin had explained
the importance of this patch for fixing the bug for x86 case in [2]. (The s390
fix is already upstream, commit id cb85a6ed67e9). Could you kindly consider
taking this fix?
[1]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1266457
[2]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1276336
fs/proc/stat.c | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 64c3b31..e296572 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int cpu)
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);
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat
2012-09-10 11:13 [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat Srivatsa S. Bhat
@ 2012-09-25 18:50 ` Srivatsa S. Bhat
0 siblings, 0 replies; 3+ messages in thread
From: Srivatsa S. Bhat @ 2012-09-25 18:50 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Ingo Molnar, mhocko, schwidefsky, deepthi, linux-kernel,
Srivatsa S. Bhat
On 09/10/2012 04:43 PM, Srivatsa S. Bhat wrote:
> From: Michal Hocko <mhocko@suse.cz>
>
> Git 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.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: stable@vger.kernel.org
> Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Signed-off-by: Michal Hocko <mhocko@suse.cz>
> [srivatsa.bhat@linux.vnet.ibm.com: Rebased to current mainline]
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---
>
> Hi Thomas,
>
> This is a resend of the patch posted by Michal at [1]. Martin had explained
> the importance of this patch for fixing the bug for x86 case in [2]. (The s390
> fix is already upstream, commit id cb85a6ed67e9). Could you kindly consider
> taking this fix?
>
Hi Thomas,
Any thoughts on this?
Regards,
Srivatsa S. Bhat
> [1]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1266457
> [2]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1276336
>
> fs/proc/stat.c | 14 ++++++++++----
> 1 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/stat.c b/fs/proc/stat.c
> index 64c3b31..e296572 100644
> --- a/fs/proc/stat.c
> +++ b/fs/proc/stat.c
> @@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int cpu)
>
> 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);
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat
@ 2012-10-10 6:21 Srivatsa S. Bhat
0 siblings, 0 replies; 3+ messages in thread
From: Srivatsa S. Bhat @ 2012-10-10 6:21 UTC (permalink / raw)
To: tglx, akpm
Cc: mhocko, mingo, schwidefsky, deepthi, linux-kernel, srivatsa.bhat
From: Michal Hocko <mhocko@suse.cz>
Git 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.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
[Srivatsa: Rebased to current mainline]
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---
This is a resend of the patch posted by Michal at [1]. Martin had explained
the importance of this patch for fixing the bug for x86 case in [2]. (The
s390 fix is already upstream, commit id cb85a6ed67e9).
[1]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1266457
[2]. http://thread.gmane.org/gmane.linux.kernel/1265374/focus=1276336
fs/proc/stat.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 64c3b31..e296572 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -45,10 +45,13 @@ static cputime64_t get_iowait_time(int cpu)
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);
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2012-09-10 11:13 [RESEND PATCH v2] nohz: fix idle ticks in cpu summary line of /proc/stat Srivatsa S. Bhat
2012-09-25 18:50 ` Srivatsa S. Bhat
2012-10-10 6:21 Srivatsa S. Bhat
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