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Date: Wed, 13 Oct 2010 06:46:18 -0700
From: Nikhil Rao <ncrao@...gle.com>
To: balbir@...ux.vnet.ibm.com
Cc: Bharata B Rao <bharata@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org,
Dhaval Giani <dhaval.giani@...il.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Pavel Emelyanov <xemul@...nvz.org>,
Herbert Poetzl <herbert@...hfloor.at>,
Avi Kivity <avi@...hat.com>,
Chris Friesen <cfriesen@...tel.com>,
Paul Menage <menage@...gle.com>,
Mike Waychison <mikew@...gle.com>, Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v3 2/7] sched: accumulate per-cfs_rq cpu usage
On Wed, Oct 13, 2010 at 6:30 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> * Bharata B Rao <bharata@...ux.vnet.ibm.com> [2010-10-12 13:21:09]:
>
>> sched: accumulate per-cfs_rq cpu usage
>>
>> From: Paul Turner <pjt@...gle.com>
>>
>> Introduce account_cfs_rq_quota() to account bandwidth usage on the cfs_rq
>> level versus task_groups for which bandwidth has been assigned. This is
>> tracked by whether the local cfs_rq->quota_assigned is finite or infinite
>> (RUNTIME_INF).
>>
>> For cfs_rq's that belong to a bandwidth constrained task_group we introduce
>> tg_request_cfs_quota() which attempts to allocate quota from the global pool
>> for use locally. Updates involving the global pool are currently protected
>> under cfs_bandwidth->lock, local pools are protected by rq->lock.
>>
>> This patch only attempts to assign and track quota, no action is taken in the
>> case that cfs_rq->quota_used exceeds cfs_rq->quota_assigned.
>>
>> Signed-off-by: Paul Turner <pjt@...gle.com>
>> Signed-off-by: Nikhil Rao <ncrao@...gle.com>
>> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
>> ---
>> include/linux/sched.h | 4 ++++
>> kernel/sched.c | 13 +++++++++++++
>> kernel/sched_fair.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> kernel/sysctl.c | 10 ++++++++++
>> 4 files changed, 77 insertions(+)
>>
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1898,6 +1898,10 @@ int sched_rt_handler(struct ctl_table *t
>> void __user *buffer, size_t *lenp,
>> loff_t *ppos);
>>
>> +#ifdef CONFIG_CFS_BANDWIDTH
>> +extern unsigned int sysctl_sched_cfs_bandwidth_slice;
>> +#endif
>> +
>> extern unsigned int sysctl_sched_compat_yield;
>>
>> #ifdef CONFIG_RT_MUTEXES
>> --- a/kernel/sched.c
>> +++ b/kernel/sched.c
>> @@ -1929,6 +1929,19 @@ static const struct sched_class rt_sched
>> * default: 0.5s
>> */
>> static u64 sched_cfs_bandwidth_period = 500000000ULL;
>> +
>> +/*
>> + * default slice of quota to allocate from global tg to local cfs_rq pool on
>> + * each refresh
>> + * default: 10ms
>> + */
>> +unsigned int sysctl_sched_cfs_bandwidth_slice = 10000UL;
>> +
>> +static inline u64 sched_cfs_bandwidth_slice(void)
>> +{
>> + return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
>> +}
>> +
>> #endif
>>
>> #define sched_class_highest (&rt_sched_class)
>> --- a/kernel/sched_fair.c
>> +++ b/kernel/sched_fair.c
>> @@ -267,6 +267,16 @@ find_matching_se(struct sched_entity **s
>>
>> #endif /* CONFIG_FAIR_GROUP_SCHED */
>>
>> +#ifdef CONFIG_CFS_BANDWIDTH
>> +static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
>> +{
>> + return &tg->cfs_bandwidth;
>> +}
>> +
>> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
>> + unsigned long delta_exec);
>> +#endif
>> +
>>
>> /**************************************************************
>> * Scheduling class tree data structure manipulation methods:
>> @@ -547,6 +557,9 @@ static void update_curr(struct cfs_rq *c
>> cpuacct_charge(curtask, delta_exec);
>> account_group_exec_runtime(curtask, delta_exec);
>> }
>> +#ifdef CONFIG_CFS_BANDWIDTH
>> + account_cfs_rq_quota(cfs_rq, delta_exec);
>> +#endif
>> }
>>
>> static inline void
>> @@ -1130,6 +1143,43 @@ static void yield_task_fair(struct rq *r
>> }
>>
>> #ifdef CONFIG_CFS_BANDWIDTH
>> +static u64 tg_request_cfs_quota(struct task_group *tg)
>> +{
>> + struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
>> + u64 delta = 0;
>> +
>> + if (cfs_b->runtime > 0 || cfs_b->quota == RUNTIME_INF) {
>
> Quick question for cfs_b->quota == RUNTIME_INF, won't cfs_b->runtime
> be always > 0?
Hi Balbir,
cfs_b->runtime can be 0 if the task group exhausts its quota.
cfs_b->runtime is a counter that is periodically refreshed to
cfs_b->quota, and is decremented every time a cfs_rq requests a slice.
-Thanks,
Nikhil
>
>> + raw_spin_lock(&cfs_b->lock);
>> + /*
>> + * it's possible a bandwidth update has changed the global
>> + * pool.
>> + */
>> + if (cfs_b->quota == RUNTIME_INF)
>> + delta = sched_cfs_bandwidth_slice();
>> + else {
>> + delta = min(cfs_b->runtime,
>> + sched_cfs_bandwidth_slice());
>> + cfs_b->runtime -= delta;
>> + }
>> + raw_spin_unlock(&cfs_b->lock);
>> + }
>> + return delta;
>> +}
>> +
>> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
>> + unsigned long delta_exec)
>> +{
>> + if (cfs_rq->quota_assigned == RUNTIME_INF)
>> + return;
>> +
>> + cfs_rq->quota_used += delta_exec;
>> +
>> + if (cfs_rq->quota_used < cfs_rq->quota_assigned)
>> + return;
>> +
>> + cfs_rq->quota_assigned += tg_request_cfs_quota(cfs_rq->tg);
>> +}
>> +
>> static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
>> {
>> return 1;
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -384,6 +384,16 @@ static struct ctl_table kern_table[] = {
>> .mode = 0644,
>> .proc_handler = proc_dointvec,
>> },
>> +#ifdef CONFIG_CFS_BANDWIDTH
>> + {
>> + .procname = "sched_cfs_bandwidth_slice_us",
>> + .data = &sysctl_sched_cfs_bandwidth_slice,
>> + .maxlen = sizeof(unsigned int),
>> + .mode = 0644,
>> + .proc_handler = proc_dointvec_minmax,
>> + .extra1 = &one,
>> + },
>> +#endif
>> #ifdef CONFIG_PROVE_LOCKING
>> {
>> .procname = "prove_locking",
>
> --
> Three Cheers,
> Balbir
>
--
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