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SubjectRe: [patch] CFS scheduler, -v14
On Wed, May 23, 2007 at 02:06:16PM +0200, Ingo Molnar wrote:
>
> i'm pleased to announce release -v14 of the CFS scheduler patchset.
>
> The CFS patch against v2.6.22-rc2, v2.6.21.1 or v2.6.20.10 can be
> downloaded from the usual place:
>
> http://people.redhat.com/mingo/cfs-scheduler/
>
> In -v14 the biggest user-visible change is increased sleeper fairness
> (done by Mike Galbraith and myself), which results in better
> interactivity under load. In particular 3D apps such as compiz/Beryl or
> games benefit from it and should be less sensitive to other apps running
> in parallel to them - but plain X benefits from it too.
>
> CFS is converging nicely, with no regressions reported against -v13.
> Changes since -v13:
>
> - increase sleeper-fairness (Mike Galbraith, me)
>
> - kernel/sched_debug.c printk argument fixes for ia64 (Andrew Morton)
>
> - CFS documentation fixes (Pranith Kumar D)
>
> - increased the default rescheduling granularity to 3msecs on UP,
> 6 msecs on 2-way systems
>
> - small update_curr() precision fix
>
> - added an overview section to Documentation/sched-design-CFS.txt
>
> - misc cleanups
>
> As usual, any sort of feedback, bugreport, fix and suggestion is more
> than welcome!
>
> Ingo

Hi, Ingo,

I've implemented a patch on top of v14 for better accounting of
sched_info statistics. Earlier, sched_info relied on jiffies for
accounting and I've seen applications that show "0" cpu usage
statistics (in delay accounting and from /proc) even though they've
been running on the CPU for a long time. The basic problem is that
accounting in jiffies is too coarse to be accurate.

The patch below uses sched_clock() for sched_info accounting.

Comments, suggestions, feedback is more than welcome!

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---
include/linux/sched.h | 10 +++++-----
kernel/delayacct.c | 10 +++++-----
kernel/sched_stats.h | 28 ++++++++++++++--------------
3 files changed, 24 insertions(+), 24 deletions(-)
diff -puN kernel/sched_stats.h~move-sched-accounting-to-sched_clock kernel/sched_stats.h
--- linux-2.6.21/kernel/sched_stats.h~move-sched-accounting-to-sched_clock 2007-05-24 11:23:38.000000000 +0530
+++ linux-2.6.21-balbir/kernel/sched_stats.h 2007-05-24 11:23:38.000000000 +0530
@@ -97,10 +97,10 @@ const struct file_operations proc_scheds
* Expects runqueue lock to be held for atomicity of update
*/
static inline void
-rq_sched_info_arrive(struct rq *rq, unsigned long delta_jiffies)
+rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
{
if (rq) {
- rq->rq_sched_info.run_delay += delta_jiffies;
+ rq->rq_sched_info.run_delay += delta;
rq->rq_sched_info.pcnt++;
}
}
@@ -109,19 +109,19 @@ rq_sched_info_arrive(struct rq *rq, unsi
* Expects runqueue lock to be held for atomicity of update
*/
static inline void
-rq_sched_info_depart(struct rq *rq, unsigned long delta_jiffies)
+rq_sched_info_depart(struct rq *rq, unsigned long long delta)
{
if (rq)
- rq->rq_sched_info.cpu_time += delta_jiffies;
+ rq->rq_sched_info.cpu_time += delta;
}
# define schedstat_inc(rq, field) do { (rq)->field++; } while (0)
# define schedstat_add(rq, field, amt) do { (rq)->field += (amt); } while (0)
#else /* !CONFIG_SCHEDSTATS */
static inline void
-rq_sched_info_arrive(struct rq *rq, unsigned long delta_jiffies)
+rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
{}
static inline void
-rq_sched_info_depart(struct rq *rq, unsigned long delta_jiffies)
+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)
@@ -155,16 +155,16 @@ static inline void sched_info_dequeued(s
*/
static void sched_info_arrive(struct task_struct *t)
{
- unsigned long now = jiffies, delta_jiffies = 0;
+ unsigned long long now = sched_clock(), delta = 0;

if (t->sched_info.last_queued)
- delta_jiffies = now - t->sched_info.last_queued;
+ delta = now - t->sched_info.last_queued;
sched_info_dequeued(t);
- t->sched_info.run_delay += delta_jiffies;
+ t->sched_info.run_delay += delta;
t->sched_info.last_arrival = now;
t->sched_info.pcnt++;

- rq_sched_info_arrive(task_rq(t), delta_jiffies);
+ rq_sched_info_arrive(task_rq(t), delta);
}

/*
@@ -186,7 +186,7 @@ static inline void sched_info_queued(str
{
if (unlikely(sched_info_on()))
if (!t->sched_info.last_queued)
- t->sched_info.last_queued = jiffies;
+ t->sched_info.last_queued = sched_clock();
}

/*
@@ -195,10 +195,10 @@ static inline void sched_info_queued(str
*/
static inline void sched_info_depart(struct task_struct *t)
{
- unsigned long delta_jiffies = jiffies - t->sched_info.last_arrival;
+ unsigned long long delta = sched_clock() - t->sched_info.last_arrival;

- t->sched_info.cpu_time += delta_jiffies;
- rq_sched_info_depart(task_rq(t), delta_jiffies);
+ t->sched_info.cpu_time += delta;
+ rq_sched_info_depart(task_rq(t), delta);
}

/*
diff -puN include/linux/sched.h~move-sched-accounting-to-sched_clock include/linux/sched.h
--- linux-2.6.21/include/linux/sched.h~move-sched-accounting-to-sched_clock 2007-05-24 11:23:38.000000000 +0530
+++ linux-2.6.21-balbir/include/linux/sched.h 2007-05-24 11:23:38.000000000 +0530
@@ -588,13 +588,13 @@ struct reclaim_state;
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
struct sched_info {
/* cumulative counters */
- unsigned long cpu_time, /* time spent on the cpu */
- run_delay, /* time spent waiting on a runqueue */
- pcnt; /* # of timeslices run on this cpu */
+ unsigned long pcnt; /* # of times run on this cpu */
+ unsigned long long cpu_time, /* time spent on the cpu */
+ run_delay; /* time spent waiting on a runqueue */

/* timestamps */
- unsigned long last_arrival, /* when we last ran on a cpu */
- last_queued; /* when we were last queued to run */
+ unsigned long long last_arrival,/* when we last ran on a cpu */
+ last_queued; /* when we were last queued to run */
};
#endif /* defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT) */

diff -puN kernel/delayacct.c~move-sched-accounting-to-sched_clock kernel/delayacct.c
--- linux-2.6.21/kernel/delayacct.c~move-sched-accounting-to-sched_clock 2007-05-24 11:31:11.000000000 +0530
+++ linux-2.6.21-balbir/kernel/delayacct.c 2007-05-24 11:52:33.000000000 +0530
@@ -99,9 +99,10 @@ void __delayacct_blkio_end(void)
int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
{
s64 tmp;
- struct timespec ts;
- unsigned long t1,t2,t3;
+ unsigned long t1;
+ unsigned long long t2,t3;
unsigned long flags;
+ struct timespec ts;

/* Though tsk->delays accessed later, early exit avoids
* unnecessary returning of other data
@@ -124,11 +125,10 @@ int __delayacct_add_tsk(struct taskstats

d->cpu_count += t1;

- jiffies_to_timespec(t2, &ts);
- tmp = (s64)d->cpu_delay_total + timespec_to_ns(&ts);
+ tmp = (s64)d->cpu_delay_total + t2;
d->cpu_delay_total = (tmp < (s64)d->cpu_delay_total) ? 0 : tmp;

- tmp = (s64)d->cpu_run_virtual_total + (s64)jiffies_to_usecs(t3) * 1000;
+ tmp = (s64)d->cpu_run_virtual_total + t3;
d->cpu_run_virtual_total =
(tmp < (s64)d->cpu_run_virtual_total) ? 0 : tmp;

_
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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