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Message-ID: <20090525132814.442877e5@dhcp-lab-109.englab.brq.redhat.com>
Date: Mon, 25 May 2009 13:28:14 +0200
From: Stanislaw Gruszka <sgruszka@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Oleg Nesterov <oleg@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
linuxppc-dev@...abs.org
Subject: Re: [PATCH resend4 2/3] itimers: fix periodic tics precision
(linuxppc-dev CC added)
On Fri, 22 May 2009 16:27:40 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:
> > if (cputime_ge(cur_time, it->expires)) {
> > - it->expires = it->incr;
> > - if (!cputime_eq(it->expires, cputime_zero))
> > - it->expires = cputime_add(it->expires, cur_time);
> > + if (!cputime_eq(it->incr, cputime_zero)) {
> > + it->expires = cputime_add(it->expires, it->incr);
> > + it->error += it->incr_error;
> > + if (it->error >= onecputick) {
> > + it->expires = cputime_sub(it->expires,
> > + jiffies_to_cputime(1));
> > + it->error -= onecputick;
> > + }
>
> Yep, that's a sane solution except for jiffies_to_cputime(), which
> can be precomputed as well.
I think precomputed is only needed for PPC where jiffies_to_cputime(1) is not
compile time constant. To not affect other architectures, I wrote a patch with
cputime_one value, it is global variable for PPC and preprocessor definition
for others. This patch is against current Linus' tree. I send it as RFC, it
was only compile tested for x86.
diff --git a/arch/ia64/include/asm/cputime.h b/arch/ia64/include/asm/cputime.h
index d20b998..df88b07 100644
--- a/arch/ia64/include/asm/cputime.h
+++ b/arch/ia64/include/asm/cputime.h
@@ -30,6 +30,7 @@ typedef u64 cputime_t;
typedef u64 cputime64_t;
#define cputime_zero ((cputime_t)0)
+#define cputime_one jiffies_to_cputime(1)
#define cputime_max ((~((cputime_t)0) >> 1) - 1)
#define cputime_add(__a, __b) ((__a) + (__b))
#define cputime_sub(__a, __b) ((__a) - (__b))
diff --git a/arch/powerpc/include/asm/cputime.h b/arch/powerpc/include/asm/cputime.h
index f42e623..e57f951 100644
--- a/arch/powerpc/include/asm/cputime.h
+++ b/arch/powerpc/include/asm/cputime.h
@@ -48,6 +48,8 @@ typedef u64 cputime64_t;
#ifdef __KERNEL__
+extern cputime_t cputime_one;
+
/*
* Convert cputime <-> jiffies
*/
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 48571ac..e46e210 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -498,6 +498,7 @@ static int __init iSeries_tb_recal(void)
tb_to_xs = divres.result_low;
vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
vdso_data->tb_to_xs = tb_to_xs;
+ cputime_one = jiffies_to_cputime(1);
}
else {
printk( "Titan recalibrate: FAILED (difference > 4 percent)\n"
@@ -904,6 +905,7 @@ void __init time_init(void)
tb_ticks_per_usec = ppc_tb_freq / 1000000;
tb_to_us = mulhwu_scale_factor(ppc_tb_freq, 1000000);
calc_cputime_factors();
+ cputime_one = jiffies_to_cputime(1);
/*
* Calculate the length of each tick in ns. It will not be
diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index 941384f..f7bbdc9 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -39,6 +39,7 @@ __div(unsigned long long n, unsigned int base)
#endif /* __s390x__ */
#define cputime_zero (0ULL)
+#define cputime_one jiffies_to_cputime(1)
#define cputime_max ((~0UL >> 1) - 1)
#define cputime_add(__a, __b) ((__a) + (__b))
#define cputime_sub(__a, __b) ((__a) - (__b))
diff --git a/include/asm-generic/cputime.h b/include/asm-generic/cputime.h
index 1c1fa42..f2b18be 100644
--- a/include/asm-generic/cputime.h
+++ b/include/asm-generic/cputime.h
@@ -7,6 +7,7 @@
typedef unsigned long cputime_t;
#define cputime_zero (0UL)
+#define cputime_one (1UL)
#define cputime_max ((~0UL >> 1) - 1)
#define cputime_add(__a, __b) ((__a) + (__b))
#define cputime_sub(__a, __b) ((__a) - (__b))
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 58762f7..ba378c6 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -65,7 +65,7 @@ int do_getitimer(int which, struct itimerval *value)
thread_group_cputimer(tsk, &cputime);
utime = cputime.utime;
if (cputime_le(cval, utime)) { /* about to fire */
- cval = jiffies_to_cputime(1);
+ cval = cputime_one;
} else {
cval = cputime_sub(cval, utime);
}
@@ -85,7 +85,7 @@ int do_getitimer(int which, struct itimerval *value)
thread_group_cputimer(tsk, ×);
ptime = cputime_add(times.utime, times.stime);
if (cputime_le(cval, ptime)) { /* about to fire */
- cval = jiffies_to_cputime(1);
+ cval = cputime_one;
} else {
cval = cputime_sub(cval, ptime);
}
@@ -182,8 +182,7 @@ again:
if (!cputime_eq(cval, cputime_zero) ||
!cputime_eq(nval, cputime_zero)) {
if (cputime_gt(nval, cputime_zero))
- nval = cputime_add(nval,
- jiffies_to_cputime(1));
+ nval = cputime_add(nval, cputime_one);
set_process_cpu_timer(tsk, CPUCLOCK_VIRT,
&nval, &cval);
}
@@ -204,8 +203,7 @@ again:
if (!cputime_eq(cval, cputime_zero) ||
!cputime_eq(nval, cputime_zero)) {
if (cputime_gt(nval, cputime_zero))
- nval = cputime_add(nval,
- jiffies_to_cputime(1));
+ nval = cputime_add(nval, cputime_one);
set_process_cpu_timer(tsk, CPUCLOCK_PROF,
&nval, &cval);
}
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index bece7c0..a86333c 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1456,7 +1456,7 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
if (!cputime_eq(*oldval, cputime_zero)) {
if (cputime_le(*oldval, now.cpu)) {
/* Just about to fire. */
- *oldval = jiffies_to_cputime(1);
+ *oldval = cputime_one;
} else {
*oldval = cputime_sub(*oldval, now.cpu);
}
diff --git a/kernel/sched.c b/kernel/sched.c
index 26efa47..b17fe3c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4726,17 +4726,16 @@ void account_idle_time(cputime_t cputime)
*/
void account_process_tick(struct task_struct *p, int user_tick)
{
- cputime_t one_jiffy = jiffies_to_cputime(1);
- cputime_t one_jiffy_scaled = cputime_to_scaled(one_jiffy);
+ cputime_t one_jiffy_scaled = cputime_to_scaled(cputime_one);
struct rq *rq = this_rq();
if (user_tick)
- account_user_time(p, one_jiffy, one_jiffy_scaled);
+ account_user_time(p, cputime_one, one_jiffy_scaled);
else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET))
- account_system_time(p, HARDIRQ_OFFSET, one_jiffy,
+ account_system_time(p, HARDIRQ_OFFSET, cputime_one,
one_jiffy_scaled);
else
- account_idle_time(one_jiffy);
+ account_idle_time(cputime_one);
}
/*
--
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