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Message-Id: <20090316103517.b0f8a20c.kamezawa.hiroyu@jp.fujitsu.com>
Date: Mon, 16 Mar 2009 10:35:17 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: bharata@...ux.vnet.ibm.com
Cc: linux-kernel@...r.kernel.org, Balaji Rao <balajirrao@...il.com>,
Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Li Zefan <lizf@...fujitsu.com>,
Paul Menage <menage@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH -tip] cpuacct: per-cgroup utime/stime statistics -
v2
On Thu, 12 Mar 2009 16:39:24 +0530
Bharata B Rao <bharata@...ux.vnet.ibm.com> wrote:
> Here is the 2nd version of the cpuacct statistics patch. Copying
> linux-arch list also this time to check if archs which define
> CONFIG_VIRT_CPU_ACCOUNTING are ok with this change.
>
> Changes for v2:
> - stime and utime now exported in clock_t units instead of msecs.
> - Addressed the code review comments from Balbir and Li Zefan.
> - Moved to -tip tree.
>
> v1:
> - http://lkml.org/lkml/2009/3/10/150
>
>
> cpuacct: Add stime and utime statistics
>
> Add per-cgroup cpuacct controller statistics like the system and user
> time consumed by the group of tasks.
>
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> Signed-off-by: Balaji Rao <balajirrao@...il.com>
> ---
> Documentation/cgroups/cpuacct.txt | 17 +++++++
> kernel/sched.c | 86 +++++++++++++++++++++++++++++++++++---
> 2 files changed, 97 insertions(+), 6 deletions(-)
>
> --- a/Documentation/cgroups/cpuacct.txt
> +++ b/Documentation/cgroups/cpuacct.txt
> @@ -30,3 +30,20 @@ The above steps create a new group g1 an
> process (bash) into it. CPU time consumed by this bash and its children
> can be obtained from g1/cpuacct.usage and the same is accumulated in
> /cgroups/cpuacct.usage also.
> +
> +cpuacct.stat file lists a few statistics which further divide the
> +CPU time obtained by the cgroup into user and system times. Currently
> +the following statistics are supported:
> +
> +utime: Time spent by tasks of the cgroup in user mode.
> +stime: Time spent by tasks of the cgroup in kernel mode.
> +
> +utime and stime are in USER_HZ unit.
> +
> +cpuacct controller uses percpu_counter interface to collect utime and
> +stime. This causes two side effects:
> +
> +- It is theoritically possible to see wrong values for stime and utime.
> + This is because percpu_counter_read() on 32bit systems is broken.
> +- It is possible to see slightly outdated values for stime and utime
> + due to the batch processing nature of percpu_counter.
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1434,10 +1434,22 @@ iter_move_one_task(struct rq *this_rq, i
> struct rq_iterator *iterator);
> #endif
>
> +/* Time spent by the tasks of the cpu accounting group executing in ... */
> +enum cpuacct_stat_index {
> + CPUACCT_STAT_UTIME, /* ... user mode */
> + CPUACCT_STAT_STIME, /* ... kernel mode */
> +
> + CPUACCT_STAT_NSTATS,
> +};
> +
> #ifdef CONFIG_CGROUP_CPUACCT
> static void cpuacct_charge(struct task_struct *tsk, u64 cputime);
> +static void cpuacct_update_stats(struct task_struct *tsk,
> + enum cpuacct_stat_index idx, cputime_t val);
> #else
> static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime) {}
> +static void cpuacct_update_stats(struct task_struct *tsk,
> + enum cpuacct_stat_index idx, cputime_t val) {}
> #endif
"static inline"
if no "inline", the complier will show warning as
"this function is defined but not used.."
> static inline void inc_cpu_load(struct rq *rq, unsigned long load)
> @@ -4379,6 +4391,8 @@ void account_user_time(struct task_struc
> cpustat->nice = cputime64_add(cpustat->nice, tmp);
> else
> cpustat->user = cputime64_add(cpustat->user, tmp);
> +
> + cpuacct_update_stats(p, CPUACCT_STAT_UTIME, cputime);
> /* Account for user time used */
> acct_update_integrals(p);
> }
> @@ -4440,6 +4454,8 @@ void account_system_time(struct task_str
> else
> cpustat->system = cputime64_add(cpustat->system, tmp);
>
> + cpuacct_update_stats(p, CPUACCT_STAT_STIME, cputime);
> +
> /* Account for system time used */
> acct_update_integrals(p);
> }
> @@ -9723,6 +9739,7 @@ struct cpuacct {
> struct cgroup_subsys_state css;
> /* cpuusage holds pointer to a u64-type object on every cpu */
> u64 *cpuusage;
> + struct percpu_counter cpustat[CPUACCT_STAT_NSTATS];
> struct cpuacct *parent;
> };
>
> @@ -9747,20 +9764,33 @@ static struct cgroup_subsys_state *cpuac
> struct cgroup_subsys *ss, struct cgroup *cgrp)
> {
> struct cpuacct *ca = kzalloc(sizeof(*ca), GFP_KERNEL);
> + int i;
>
> if (!ca)
> - return ERR_PTR(-ENOMEM);
> + goto out;
>
> ca->cpuusage = alloc_percpu(u64);
> - if (!ca->cpuusage) {
> - kfree(ca);
> - return ERR_PTR(-ENOMEM);
> - }
> + if (!ca->cpuusage)
> + goto out_free_ca;
> +
> + for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
> + if (percpu_counter_init(&ca->cpustat[i], 0))
> + goto out_free_counters;
>
> if (cgrp->parent)
> ca->parent = cgroup_ca(cgrp->parent);
>
> return &ca->css;
> +
> +out_free_counters:
> + i--;
> + while (i-- >= 0)
> + percpu_counter_destroy(&ca->cpustat[i]);
> + free_percpu(ca->cpuusage);
> +out_free_ca:
> + kfree(ca);
> +out:
> + return ERR_PTR(-ENOMEM);
> }
>
> /* destroy an existing cpu accounting group */
> @@ -9768,7 +9798,10 @@ static void
> cpuacct_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
> {
> struct cpuacct *ca = cgroup_ca(cgrp);
> + int i;
>
> + for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
> + percpu_counter_destroy(&ca->cpustat[i]);
> free_percpu(ca->cpuusage);
> kfree(ca);
> }
> @@ -9855,6 +9888,25 @@ static int cpuacct_percpu_seq_read(struc
> return 0;
> }
>
> +static const char *cpuacct_stat_desc[] = {
> + [CPUACCT_STAT_UTIME] = "utime",
> + [CPUACCT_STAT_STIME] = "stime",
> +};
> +
> +static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft,
> + struct cgroup_map_cb *cb)
> +{
> + struct cpuacct *ca = cgroup_ca(cgrp);
> + int i;
> +
> + for (i = 0; i < CPUACCT_STAT_NSTATS; i++) {
> + s64 val = percpu_counter_read(&ca->cpustat[i]);
> + val = cputime_to_clock_t(val);
> + cb->fill(cb, cpuacct_stat_desc[i], val);
> + }
> + return 0;
> +}
> +
> static struct cftype files[] = {
> {
> .name = "usage",
> @@ -9865,7 +9917,10 @@ static struct cftype files[] = {
> .name = "usage_percpu",
> .read_seq_string = cpuacct_percpu_seq_read,
> },
> -
> + {
> + .name = "stat",
> + .read_map = cpuacct_stats_show,
> + },
> };
>
> static int cpuacct_populate(struct cgroup_subsys *ss, struct cgroup *cgrp)
> @@ -9895,6 +9950,25 @@ static void cpuacct_charge(struct task_s
> }
> }
>
> +/*
> + * Account the system/user time to the task's accounting group.
> + */
> +static void cpuacct_update_stats(struct task_struct *tsk,
> + enum cpuacct_stat_index idx, cputime_t val)
> +{
> + struct cpuacct *ca;
> +
> + if (unlikely(!cpuacct_subsys.active))
> + return;
> +
> + ca = task_ca(tsk);
> +
> + do {
> + percpu_counter_add(&ca->cpustat[idx], val);
> + ca = ca->parent;
> + } while (ca);
> +}
> +
IIUC, to make sure accessing "ca" to be safe, we need some condition.
(task_lock() or some other.....
Could you add "why this is safe ?" as comment ?
-Kame
> struct cgroup_subsys cpuacct_subsys = {
> .name = "cpuacct",
> .create = cpuacct_create,
> --
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