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Date: Mon, 15 Jun 2009 10:55:42 +0200
From: Stanislaw Gruszka <sgruszka@...hat.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Thomas Gleixner <tglx@...utronix.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC PATCH] posix-cpu-timers: optimize calling
thread_group_cputime()
On Fri, 12 Jun 2009 16:25:46 +0200
Oleg Nesterov <oleg@...hat.com> wrote:
> To clarify, I am not arguing against this patch, just a queston.
>
> On 06/12, Stanislaw Gruszka wrote:
> >
> > On Fri, 12 Jun 2009 13:09:46 +0200
> > Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> >
> > > On Fri, 2009-06-12 at 12:39 +0200, Stanislaw Gruszka wrote:
> > > > - times->utime = cputime_add(times->utime, t->utime);
> > > > - times->stime = cputime_add(times->stime, t->stime);
> > > > - times->sum_exec_runtime += t->se.sum_exec_runtime;
> > > > + if (mask & TG_CPUCLOCK_UTIME)
> > > > + times->utime = cputime_add(times->utime, t->utime);
> > > > + if (mask & TG_CPUCLOCK_STIME)
> > > > + times->stime = cputime_add(times->stime, t->stime);
> > > > + if (mask & TG_CPUCLOCK_SCHED)
> > > > + times->sum_exec_runtime += t->se.sum_exec_runtime;
> > >
> > > Does adding 3 branches really make it faster?
> > Actually I did not any benchmarking yet, so I don't know what is the real
> > impact of the patch. I hope it make things taster but the result can be
> > opposite from my expectations.
>
> I agree with Peter, if we complicate the code it would be nice to know
> this really makes it faster. Besides, thread_group_cputime() should not
> be called that often.
I did some benchmarking, I don't think further the patch is good, it not get
speed up I expected for clock_gettime().
First was measurement of thread_group_cycles() [1] with standart usage when is
called from posix_cpu_timers_exit_group():
Without patch:
tg_cputime_cycles 1524672
tg_cputime_n 6246
average: 244 cycles
With patch:
tg_cputime_cycles 1593876
tg_cputime_n 6368
average: 250 cycles
Second benchmark measure time of 250 thread process which do lots of
clock_gettime(), here are results:
Without patch:
[stasiu@...p-lab-195 Work]$ ./bench_getclock
CLK_PROF: 0.387411
CLK_VIRT: 0.371487
CLK_SCHED: 0.396650
With patch:
[stasiu@...p-lab-195 Work]$ ./bench_getclock
CLK_PROF: 0.336056
CLK_VIRT: 0.305781
CLK_SCHED: 0.339739
[1] Patch to measure thread_group_cputime() cycles:
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 81e4eb6..14021e8 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -22,6 +22,9 @@
#define arch_idle_time(cpu) 0
#endif
+extern unsigned long long tg_cputime_cycles;
+extern unsigned long tg_cputime_n;
+
static int show_stat(struct seq_file *p, void *v)
{
int i, j;
@@ -108,12 +111,16 @@ static int show_stat(struct seq_file *p, void *v)
"btime %lu\n"
"processes %lu\n"
"procs_running %lu\n"
- "procs_blocked %lu\n",
+ "procs_blocked %lu\n"
+ "tg_cputime_cycles %llu\n"
+ "tg_cputime_n %lu\n",
nr_context_switches(),
(unsigned long)jif,
total_forks,
nr_running(),
- nr_iowait());
+ nr_iowait(),
+ tg_cputime_cycles,
+ tg_cputime_n);
return 0;
}
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index b5f1b44..6ff946c 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -230,13 +230,20 @@ static int cpu_clock_sample(const clockid_t which_clock, struct task_struct *p,
return 0;
}
+unsigned long long tg_cputime_cycles;
+unsigned long tg_cputime_n;
+
void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times,
int mask)
{
struct sighand_struct *sighand;
struct signal_struct *sig;
struct task_struct *t;
+ unsigned long long xstart, xend;
+ xstart = get_cycles();
+ barrier();
+
*times = INIT_CPUTIME;
rcu_read_lock();
@@ -266,6 +273,11 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times,
times->sum_exec_runtime += sig->sum_sched_runtime;
out:
rcu_read_unlock();
+
+ barrier();
+ xend = get_cycles();
+ tg_cputime_cycles += xend - xstart;
+ tg_cputime_n++;
}
static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
[2] Benchmark multithread process clock_gettime():
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <unistd.h>
#define CPUCLOCK_PROF 0
#define CPUCLOCK_VIRT 1
#define CPUCLOCK_SCHED 2
#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
((~(clockid_t) (pid) << 3) | (clockid_t) (clock))
#define CLK_PROF MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_PROF)
#define CLK_VIRT MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_VIRT)
#define CLK_SCHED MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED)
#define NTHREADS 250
void *thread_main(void *dummy)
{
while (1)
sleep(100);
}
void create_threads(void)
{
int i, rc;
pthread_t tid;
pthread_attr_t attr;
pthread_attr_init(&attr);
for (i = 0; i < NTHREADS; i++) {
rc = pthread_create(&tid, &attr, thread_main, NULL);
if (rc) {
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
}
double timeval_diff(const struct timeval *start, const struct timeval *end)
{
return (end->tv_sec - start->tv_sec) + (end->tv_usec - start->tv_usec)/1000000.0;
}
void bench(clockid_t cid, char *str)
{
int i;
struct timespec ts;
struct timeval start, end;
double t;
gettimeofday(&start, NULL);
for (i = 0; i < 100000; i++)
clock_gettime(cid, &ts);
gettimeofday(&end, NULL);
t = timeval_diff(&start, &end);
printf("%s: %f\n", str, t);
}
int main(void)
{
create_threads();
bench(CLK_PROF, "CLK_PROF");
bench(CLK_VIRT, "CLK_VIRT");
bench(CLK_SCHED, "CLK_SCHED");
return 0;
}
--
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