cpuacct has 2 different ways of accounting and showing user
and system times.
The first one uses cpuacct_account_field() to account times
and cpuacct.stat file to expose them. And this one seems to work ok.
The second one is uses cpuacct_charge() function for accounting and
set of cpuacct.usage* files to show times. Despite some attempts to
fix it in the past it still doesn't work. E.g. while running KVM
guest the cpuacct_charge() accounts most of the guest time as
system time. This doesn't match with user&system times shown in
cpuacct.stat or proc/<pid>/stat.
Use cpustats accounted in cpuacct_account_field() as the source
of user/sys times for cpuacct.usage* files. Make cpuacct_charge()
to account only summary execution time.
Fixes: d740037fac70 ("sched/cpuacct: Split usage accounting into user_usage and sys_usage")
Signed-off-by: Andrey Ryabinin <[email protected]>
Cc: <[email protected]>
---
kernel/sched/cpuacct.c | 77 +++++++++++++++++++-----------------------
1 file changed, 34 insertions(+), 43 deletions(-)
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 941c28cf9738..7eff79faab0d 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -29,7 +29,7 @@ struct cpuacct_usage {
struct cpuacct {
struct cgroup_subsys_state css;
/* cpuusage holds pointer to a u64-type object on every CPU */
- struct cpuacct_usage __percpu *cpuusage;
+ u64 __percpu *cpuusage;
struct kernel_cpustat __percpu *cpustat;
};
@@ -49,7 +49,7 @@ static inline struct cpuacct *parent_ca(struct cpuacct *ca)
return css_ca(ca->css.parent);
}
-static DEFINE_PER_CPU(struct cpuacct_usage, root_cpuacct_cpuusage);
+static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
static struct cpuacct root_cpuacct = {
.cpustat = &kernel_cpustat,
.cpuusage = &root_cpuacct_cpuusage,
@@ -68,7 +68,7 @@ cpuacct_css_alloc(struct cgroup_subsys_state *parent_css)
if (!ca)
goto out;
- ca->cpuusage = alloc_percpu(struct cpuacct_usage);
+ ca->cpuusage = alloc_percpu(u64);
if (!ca->cpuusage)
goto out_free_ca;
@@ -99,7 +99,8 @@ static void cpuacct_css_free(struct cgroup_subsys_state *css)
static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu,
enum cpuacct_stat_index index)
{
- struct cpuacct_usage *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
+ u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
+ u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
u64 data;
/*
@@ -115,14 +116,17 @@ static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu,
raw_spin_lock_irq(&cpu_rq(cpu)->lock);
#endif
- if (index == CPUACCT_STAT_NSTATS) {
- int i = 0;
-
- data = 0;
- for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
- data += cpuusage->usages[i];
- } else {
- data = cpuusage->usages[index];
+ switch (index) {
+ case CPUACCT_STAT_USER:
+ data = cpustat[CPUTIME_USER] + cpustat[CPUTIME_NICE];
+ break;
+ case CPUACCT_STAT_SYSTEM:
+ data = cpustat[CPUTIME_SYSTEM] + cpustat[CPUTIME_IRQ] +
+ cpustat[CPUTIME_SOFTIRQ];
+ break;
+ case CPUACCT_STAT_NSTATS:
+ data = *cpuusage;
+ break;
}
#ifndef CONFIG_64BIT
@@ -132,10 +136,14 @@ static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu,
return data;
}
-static void cpuacct_cpuusage_write(struct cpuacct *ca, int cpu, u64 val)
+static void cpuacct_cpuusage_write(struct cpuacct *ca, int cpu)
{
- struct cpuacct_usage *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
- int i;
+ u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
+ u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
+
+ /* Don't allow to reset global kernel_cpustat */
+ if (ca == &root_cpuacct)
+ return;
#ifndef CONFIG_64BIT
/*
@@ -143,9 +151,10 @@ static void cpuacct_cpuusage_write(struct cpuacct *ca, int cpu, u64 val)
*/
raw_spin_lock_irq(&cpu_rq(cpu)->lock);
#endif
-
- for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
- cpuusage->usages[i] = val;
+ *cpuusage = 0;
+ cpustat[CPUTIME_USER] = cpustat[CPUTIME_NICE] = 0;
+ cpustat[CPUTIME_SYSTEM] = cpustat[CPUTIME_IRQ] = 0;
+ cpustat[CPUTIME_SOFTIRQ] = 0;
#ifndef CONFIG_64BIT
raw_spin_unlock_irq(&cpu_rq(cpu)->lock);
@@ -196,7 +205,7 @@ static int cpuusage_write(struct cgroup_subsys_state *css, struct cftype *cft,
return -EINVAL;
for_each_possible_cpu(cpu)
- cpuacct_cpuusage_write(ca, cpu, 0);
+ cpuacct_cpuusage_write(ca, cpu);
return 0;
}
@@ -243,25 +252,12 @@ static int cpuacct_all_seq_show(struct seq_file *m, void *V)
seq_puts(m, "\n");
for_each_possible_cpu(cpu) {
- struct cpuacct_usage *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
-
seq_printf(m, "%d", cpu);
- for (index = 0; index < CPUACCT_STAT_NSTATS; index++) {
-#ifndef CONFIG_64BIT
- /*
- * Take rq->lock to make 64-bit read safe on 32-bit
- * platforms.
- */
- raw_spin_lock_irq(&cpu_rq(cpu)->lock);
-#endif
-
- seq_printf(m, " %llu", cpuusage->usages[index]);
+ for (index = 0; index < CPUACCT_STAT_NSTATS; index++)
+ seq_printf(m, " %llu",
+ cpuacct_cpuusage_read(ca, cpu, index));
-#ifndef CONFIG_64BIT
- raw_spin_unlock_irq(&cpu_rq(cpu)->lock);
-#endif
- }
seq_puts(m, "\n");
}
return 0;
@@ -278,8 +274,8 @@ static int cpuacct_stats_show(struct seq_file *sf, void *v)
for_each_possible_cpu(cpu) {
u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
- val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
- val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
+ val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
+ val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
val[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_SYSTEM];
val[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_IRQ];
val[CPUACCT_STAT_SYSTEM] += cpustat[CPUTIME_SOFTIRQ];
@@ -339,16 +335,11 @@ static struct cftype files[] = {
void cpuacct_charge(struct task_struct *tsk, u64 cputime)
{
struct cpuacct *ca;
- int index = CPUACCT_STAT_SYSTEM;
- struct pt_regs *regs = get_irq_regs() ? : task_pt_regs(tsk);
-
- if (regs && user_mode(regs))
- index = CPUACCT_STAT_USER;
rcu_read_lock();
for (ca = task_ca(tsk); ca; ca = parent_ca(ca))
- __this_cpu_add(ca->cpuusage->usages[index], cputime);
+ __this_cpu_add(*ca->cpuusage, cputime);
rcu_read_unlock();
}
--
2.26.2
Andrey Ryabinin <[email protected]> writes:
> cpuacct has 2 different ways of accounting and showing user
> and system times.
>
> The first one uses cpuacct_account_field() to account times
> and cpuacct.stat file to expose them. And this one seems to work ok.
>
> The second one is uses cpuacct_charge() function for accounting and
> set of cpuacct.usage* files to show times. Despite some attempts to
> fix it in the past it still doesn't work. E.g. while running KVM
> guest the cpuacct_charge() accounts most of the guest time as
> system time. This doesn't match with user&system times shown in
> cpuacct.stat or proc/<pid>/stat.
I couldn't reproduce this running a cpu bound load in a kvm guest on a
nohz_full cpu on 5.11. The time is almost entirely in cpuacct.usage and
_user, while _sys stays low.
Could you say more about how you're seeing this? Don't really doubt
there's a problem, just wondering what you're doing.
> diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
> index 941c28cf9738..7eff79faab0d 100644
> --- a/kernel/sched/cpuacct.c
> +++ b/kernel/sched/cpuacct.c
> @@ -29,7 +29,7 @@ struct cpuacct_usage {
> struct cpuacct {
> struct cgroup_subsys_state css;
> /* cpuusage holds pointer to a u64-type object on every CPU */
> - struct cpuacct_usage __percpu *cpuusage;
Definition of struct cpuacct_usage can go away now.
> @@ -99,7 +99,8 @@ static void cpuacct_css_free(struct cgroup_subsys_state *css)
> static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu,
> enum cpuacct_stat_index index)
> {
> - struct cpuacct_usage *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
> + u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
> + u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
> u64 data;
There's a BUG_ON below this that could probably be WARN_ON_ONCE while
you're here
> @@ -278,8 +274,8 @@ static int cpuacct_stats_show(struct seq_file *sf, void *v)
> for_each_possible_cpu(cpu) {
> u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
>
> - val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
> - val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
> + val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
> + val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
unnecessary whitespace change?
On 3/18/21 1:22 AM, Daniel Jordan wrote:
> Andrey Ryabinin <[email protected]> writes:
>
>> cpuacct has 2 different ways of accounting and showing user
>> and system times.
>>
>> The first one uses cpuacct_account_field() to account times
>> and cpuacct.stat file to expose them. And this one seems to work ok.
>>
>> The second one is uses cpuacct_charge() function for accounting and
>> set of cpuacct.usage* files to show times. Despite some attempts to
>> fix it in the past it still doesn't work. E.g. while running KVM
>> guest the cpuacct_charge() accounts most of the guest time as
>> system time. This doesn't match with user&system times shown in
>> cpuacct.stat or proc/<pid>/stat.
>
> I couldn't reproduce this running a cpu bound load in a kvm guest on a
> nohz_full cpu on 5.11. The time is almost entirely in cpuacct.usage and
> _user, while _sys stays low.
>
> Could you say more about how you're seeing this? Don't really doubt
> there's a problem, just wondering what you're doing.
>
Yeah, I it's almost unnoticable if you run some load in guest like qemu.
But more simple case with busy loop in KVM_RUN triggers this:
# git clone https://github.com/aryabinin/kvmsample
# make
# mkdir /sys/fs/cgroup/cpuacct/test
# echo $$ > /sys/fs/cgroup/cpuacct/test/tasks
# ./kvmsample &
# for i in {1..5}; do cat /sys/fs/cgroup/cpuacct/test/cpuacct.usage_sys; sleep 1; done
1976535645
2979839428
3979832704
4983603153
5983604157
>> diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
>> index 941c28cf9738..7eff79faab0d 100644
>> --- a/kernel/sched/cpuacct.c
>> +++ b/kernel/sched/cpuacct.c
>> @@ -29,7 +29,7 @@ struct cpuacct_usage {
>> struct cpuacct {
>> struct cgroup_subsys_state css;
>> /* cpuusage holds pointer to a u64-type object on every CPU */
>> - struct cpuacct_usage __percpu *cpuusage;
>
> Definition of struct cpuacct_usage can go away now.
>
Done.
>> @@ -99,7 +99,8 @@ static void cpuacct_css_free(struct cgroup_subsys_state *css)
>> static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu,
>> enum cpuacct_stat_index index)
>> {
>> - struct cpuacct_usage *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
>> + u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
>> + u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
>> u64 data;
>
> There's a BUG_ON below this that could probably be WARN_ON_ONCE while
> you're here
>
Sure.
>> @@ -278,8 +274,8 @@ static int cpuacct_stats_show(struct seq_file *sf, void *v)
>> for_each_possible_cpu(cpu) {
>> u64 *cpustat = per_cpu_ptr(ca->cpustat, cpu)->cpustat;
>>
>> - val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
>> - val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
>> + val[CPUACCT_STAT_USER] += cpustat[CPUTIME_USER];
>> + val[CPUACCT_STAT_USER] += cpustat[CPUTIME_NICE];
>
> unnecessary whitespace change?
>
yup