linux_dsm_epyc7002/kernel/sched/stats.h
Jason Low 1018016c70 sched, timer: Replace spinlocks with atomics in thread_group_cputimer(), to improve scalability
While running a database workload, we found a scalability issue with itimers.

Much of the problem was caused by the thread_group_cputimer spinlock.
Each time we account for group system/user time, we need to obtain a
thread_group_cputimer's spinlock to update the timers. On larger systems
(such as a 16 socket machine), this caused more than 30% of total time
spent trying to obtain this kernel lock to update these group timer stats.

This patch converts the timers to 64-bit atomic variables and use
atomic add to update them without a lock. With this patch, the percent
of total time spent updating thread group cputimer timers was reduced
from 30% down to less than 1%.

Note: On 32-bit systems using the generic 64-bit atomics, this causes
sample_group_cputimer() to take locks 3 times instead of just 1 time.
However, we tested this patch on a 32-bit system ARM system using the
generic atomics and did not find the overhead to be much of an issue.
An explanation for why this isn't an issue is that 32-bit systems usually
have small numbers of CPUs, and cacheline contention from extra spinlocks
called periodically is not really apparent on smaller systems.

Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Waiman Long <Waiman.Long@hp.com>
Link: http://lkml.kernel.org/r/1430251224-5764-4-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-05-08 12:15:31 +02:00

263 lines
7.7 KiB
C

#ifdef CONFIG_SCHEDSTATS
/*
* Expects runqueue lock to be held for atomicity of update
*/
static inline void
rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
{
if (rq) {
rq->rq_sched_info.run_delay += delta;
rq->rq_sched_info.pcount++;
}
}
/*
* Expects runqueue lock to be held for atomicity of update
*/
static inline void
rq_sched_info_depart(struct rq *rq, unsigned long long delta)
{
if (rq)
rq->rq_cpu_time += delta;
}
static inline void
rq_sched_info_dequeued(struct rq *rq, unsigned long long delta)
{
if (rq)
rq->rq_sched_info.run_delay += delta;
}
# define schedstat_inc(rq, field) do { (rq)->field++; } while (0)
# define schedstat_add(rq, field, amt) do { (rq)->field += (amt); } while (0)
# define schedstat_set(var, val) do { var = (val); } while (0)
#else /* !CONFIG_SCHEDSTATS */
static inline void
rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
{}
static inline void
rq_sched_info_dequeued(struct rq *rq, unsigned long long delta)
{}
static inline void
rq_sched_info_depart(struct rq *rq, unsigned long long delta)
{}
# define schedstat_inc(rq, field) do { } while (0)
# define schedstat_add(rq, field, amt) do { } while (0)
# define schedstat_set(var, val) do { } while (0)
#endif
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
static inline void sched_info_reset_dequeued(struct task_struct *t)
{
t->sched_info.last_queued = 0;
}
/*
* We are interested in knowing how long it was from the *first* time a
* task was queued to the time that it finally hit a cpu, we call this routine
* from dequeue_task() to account for possible rq->clock skew across cpus. The
* delta taken on each cpu would annul the skew.
*/
static inline void sched_info_dequeued(struct rq *rq, struct task_struct *t)
{
unsigned long long now = rq_clock(rq), delta = 0;
if (unlikely(sched_info_on()))
if (t->sched_info.last_queued)
delta = now - t->sched_info.last_queued;
sched_info_reset_dequeued(t);
t->sched_info.run_delay += delta;
rq_sched_info_dequeued(rq, delta);
}
/*
* Called when a task finally hits the cpu. We can now calculate how
* long it was waiting to run. We also note when it began so that we
* can keep stats on how long its timeslice is.
*/
static void sched_info_arrive(struct rq *rq, struct task_struct *t)
{
unsigned long long now = rq_clock(rq), delta = 0;
if (t->sched_info.last_queued)
delta = now - t->sched_info.last_queued;
sched_info_reset_dequeued(t);
t->sched_info.run_delay += delta;
t->sched_info.last_arrival = now;
t->sched_info.pcount++;
rq_sched_info_arrive(rq, delta);
}
/*
* This function is only called from enqueue_task(), but also only updates
* the timestamp if it is already not set. It's assumed that
* sched_info_dequeued() will clear that stamp when appropriate.
*/
static inline void sched_info_queued(struct rq *rq, struct task_struct *t)
{
if (unlikely(sched_info_on()))
if (!t->sched_info.last_queued)
t->sched_info.last_queued = rq_clock(rq);
}
/*
* Called when a process ceases being the active-running process involuntarily
* due, typically, to expiring its time slice (this may also be called when
* switching to the idle task). Now we can calculate how long we ran.
* Also, if the process is still in the TASK_RUNNING state, call
* sched_info_queued() to mark that it has now again started waiting on
* the runqueue.
*/
static inline void sched_info_depart(struct rq *rq, struct task_struct *t)
{
unsigned long long delta = rq_clock(rq) -
t->sched_info.last_arrival;
rq_sched_info_depart(rq, delta);
if (t->state == TASK_RUNNING)
sched_info_queued(rq, t);
}
/*
* Called when tasks are switched involuntarily due, typically, to expiring
* their time slice. (This may also be called when switching to or from
* the idle task.) We are only called when prev != next.
*/
static inline void
__sched_info_switch(struct rq *rq,
struct task_struct *prev, struct task_struct *next)
{
/*
* prev now departs the cpu. It's not interesting to record
* stats about how efficient we were at scheduling the idle
* process, however.
*/
if (prev != rq->idle)
sched_info_depart(rq, prev);
if (next != rq->idle)
sched_info_arrive(rq, next);
}
static inline void
sched_info_switch(struct rq *rq,
struct task_struct *prev, struct task_struct *next)
{
if (unlikely(sched_info_on()))
__sched_info_switch(rq, prev, next);
}
#else
#define sched_info_queued(rq, t) do { } while (0)
#define sched_info_reset_dequeued(t) do { } while (0)
#define sched_info_dequeued(rq, t) do { } while (0)
#define sched_info_depart(rq, t) do { } while (0)
#define sched_info_arrive(rq, next) do { } while (0)
#define sched_info_switch(rq, t, next) do { } while (0)
#endif /* CONFIG_SCHEDSTATS || CONFIG_TASK_DELAY_ACCT */
/*
* The following are functions that support scheduler-internal time accounting.
* These functions are generally called at the timer tick. None of this depends
* on CONFIG_SCHEDSTATS.
*/
/**
* cputimer_running - return true if cputimer is running
*
* @tsk: Pointer to target task.
*/
static inline bool cputimer_running(struct task_struct *tsk)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
/* Check if cputimer isn't running. This is accessed without locking. */
if (!READ_ONCE(cputimer->running))
return false;
/*
* After we flush the task's sum_exec_runtime to sig->sum_sched_runtime
* in __exit_signal(), we won't account to the signal struct further
* cputime consumed by that task, even though the task can still be
* ticking after __exit_signal().
*
* In order to keep a consistent behaviour between thread group cputime
* and thread group cputimer accounting, lets also ignore the cputime
* elapsing after __exit_signal() in any thread group timer running.
*
* This makes sure that POSIX CPU clocks and timers are synchronized, so
* that a POSIX CPU timer won't expire while the corresponding POSIX CPU
* clock delta is behind the expiring timer value.
*/
if (unlikely(!tsk->sighand))
return false;
return true;
}
/**
* account_group_user_time - Maintain utime for a thread group.
*
* @tsk: Pointer to task structure.
* @cputime: Time value by which to increment the utime field of the
* thread_group_cputime structure.
*
* If thread group time is being maintained, get the structure for the
* running CPU and update the utime field there.
*/
static inline void account_group_user_time(struct task_struct *tsk,
cputime_t cputime)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
if (!cputimer_running(tsk))
return;
atomic64_add(cputime, &cputimer->utime);
}
/**
* account_group_system_time - Maintain stime for a thread group.
*
* @tsk: Pointer to task structure.
* @cputime: Time value by which to increment the stime field of the
* thread_group_cputime structure.
*
* If thread group time is being maintained, get the structure for the
* running CPU and update the stime field there.
*/
static inline void account_group_system_time(struct task_struct *tsk,
cputime_t cputime)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
if (!cputimer_running(tsk))
return;
atomic64_add(cputime, &cputimer->stime);
}
/**
* account_group_exec_runtime - Maintain exec runtime for a thread group.
*
* @tsk: Pointer to task structure.
* @ns: Time value by which to increment the sum_exec_runtime field
* of the thread_group_cputime structure.
*
* If thread group time is being maintained, get the structure for the
* running CPU and update the sum_exec_runtime field there.
*/
static inline void account_group_exec_runtime(struct task_struct *tsk,
unsigned long long ns)
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
if (!cputimer_running(tsk))
return;
atomic64_add(ns, &cputimer->sum_exec_runtime);
}