Re: [PATCH] s390 (9/9): no timer interrupts in idle.

From: Martin Schwidefsky
Date: Wed Apr 21 2004 - 14:00:02 EST

Hi Christoph,
new patch with your suggestions. I compiled a kernel for i386. The
code for rcu_start_batch isn't identical but it didn't looked too
bad either. I still think a #ifdef in rcpu_start_batch would help.
Any more comments ?

blue skies,
Martin.

---
[PATCH] s390: no timer interrupts in idle.

From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

This patch add a system control that allows to switch off the jiffies
timer interrupts while a cpu sleeps in idle. This is useful for a system
running with virtual cpus under z/VM.

diffstat:
arch/s390/Kconfig | 19 +++++
arch/s390/defconfig | 1
arch/s390/kernel/process.c | 10 +-
arch/s390/kernel/time.c | 158 ++++++++++++++++++++++++++++++++++++++-------
arch/s390/kernel/traps.c | 4 -
include/asm-s390/cpumask.h | 3
include/linux/sysctl.h | 1
include/linux/timer.h | 2
kernel/rcupdate.c | 9 ++
kernel/sysctl.c | 12 +++
kernel/timer.c | 69 +++++++++++++++++++
11 files changed, 259 insertions(+), 29 deletions(-)

diff -urN linux-2.6/arch/s390/Kconfig linux-2.6-s390/arch/s390/Kconfig
--- linux-2.6/arch/s390/Kconfig Wed Apr 21 20:25:32 2004
+++ linux-2.6-s390/arch/s390/Kconfig Wed Apr 21 20:25:33 2004
@@ -333,6 +333,25 @@
This can also be compiled as a module, which will be called
appldata_net_sum.o.

+config NO_IDLE_HZ
+ bool "No HZ timer ticks in idle"
+ help
+ Switches the regular HZ timer off when the system is going idle.
+ This helps z/VM to detect that the Linux system is idle. VM can
+ then "swap-out" this guest which reduces memory usage. It also
+ reduces the overhead of idle systems.
+
+ The HZ timer can be switched on/off via /proc/sys/kernel/hz_timer.
+ hz_timer=0 means HZ timer is disabled. hz_timer=1 means HZ
+ timer is active.
+
+config NO_IDLE_HZ_INIT
+ bool "HZ timer in idle off by default"
+ depends on NO_IDLE_HZ
+ help
+ The HZ timer is switched off in idle by default. That means the
+ HZ timer is already disabled at boot time.
+
endmenu

config PCMCIA
diff -urN linux-2.6/arch/s390/defconfig linux-2.6-s390/arch/s390/defconfig
--- linux-2.6/arch/s390/defconfig Wed Apr 21 20:25:33 2004
+++ linux-2.6-s390/arch/s390/defconfig Wed Apr 21 20:25:58 2004
@@ -83,6 +83,7 @@
# CONFIG_SHARED_KERNEL is not set
# CONFIG_CMM is not set
# CONFIG_VIRT_TIMER is not set
+# CONFIG_NO_IDLE_HZ is not set
# CONFIG_PCMCIA is not set

#
diff -urN linux-2.6/arch/s390/kernel/process.c linux-2.6-s390/arch/s390/kernel/process.c
--- linux-2.6/arch/s390/kernel/process.c Wed Apr 21 20:25:05 2004
+++ linux-2.6-s390/arch/s390/kernel/process.c Wed Apr 21 20:25:33 2004
@@ -40,7 +40,7 @@
#include <asm/io.h>
#include <asm/processor.h>
#include <asm/irq.h>
-#ifdef CONFIG_VIRT_TIMER
+#if defined(CONFIG_VIRT_TIMER) || defined (CONFIG_NO_IDLE_HZ)
#include <asm/timer.h>
#endif

@@ -75,17 +75,21 @@
psw_t wait_psw;
unsigned long reg;

+ local_irq_disable();
if (need_resched()) {
+ local_irq_enable();
schedule();
return;
}

-#ifdef CONFIG_VIRT_TIMER
+#if defined(CONFIG_VIRT_TIMER) || defined (CONFIG_NO_IDLE_HZ)
/*
* hook to stop timers that should not tick while CPU is idle
*/
- if (stop_timers())
+ if (stop_timers()) {
+ local_irq_enable();
return;
+ }
#endif

/*
diff -urN linux-2.6/arch/s390/kernel/time.c linux-2.6-s390/arch/s390/kernel/time.c
--- linux-2.6/arch/s390/kernel/time.c Wed Apr 21 20:25:32 2004
+++ linux-2.6-s390/arch/s390/kernel/time.c Wed Apr 21 20:25:33 2004
@@ -331,29 +331,6 @@
return 0;
}

-void do_monitor_call(struct pt_regs *regs, long interruption_code)
-{
- /* disable monitor call class 0 */
- __ctl_clear_bit(8, 15);
-
- start_cpu_timer();
-}
-
-/*
- * called from cpu_idle to stop any timers
- * returns 1 if CPU should not be stopped
- */
-int stop_timers(void)
-{
- if (stop_cpu_timer())
- return 1;
-
- /* enable monitor call class 0 */
- __ctl_set_bit(8, 15);
-
- return 0;
-}
-
void set_vtimer(__u64 expires)
{
asm volatile ("SPT %0" : : "m" (expires));
@@ -474,6 +451,141 @@
}
#endif

+#ifdef CONFIG_NO_IDLE_HZ
+
+cpumask_t idle_cpu_mask = CPU_MASK_NONE;
+
+#ifdef CONFIG_NO_IDLE_HZ_INIT
+int sysctl_hz_timer = 0;
+#else
+int sysctl_hz_timer = 1;
+#endif
+
+/*
+ * Start the HZ tick on the current CPU.
+ * Only cpu_idle may call this function.
+ */
+void start_hz_timer(struct pt_regs *regs)
+{
+ __u64 tmp;
+ __u32 ticks;
+
+ if (!cpu_isset(smp_processor_id(), idle_cpu_mask))
+ return;
+
+ /* Calculate how many ticks have passed */
+ asm volatile ("STCK 0(%0)" : : "a" (&tmp) : "memory", "cc");
+ tmp = tmp + CLK_TICKS_PER_JIFFY - S390_lowcore.jiffy_timer;
+ ticks = __calculate_ticks(tmp);
+ S390_lowcore.jiffy_timer += CLK_TICKS_PER_JIFFY * (__u64) ticks;
+
+ /* Set the clock comparator to the next tick. */
+ tmp = S390_lowcore.jiffy_timer + CPU_DEVIATION;
+ asm volatile ("SCKC %0" : : "m" (tmp));
+
+ /* Charge the ticks. */
+ if (ticks > 0) {
+#ifdef CONFIG_SMP
+ /*
+ * Do not rely on the boot cpu to do the calls to do_timer.
+ * Spread it over all cpus instead.
+ */
+ write_seqlock(&xtime_lock);
+ if (S390_lowcore.jiffy_timer > xtime_cc) {
+ __u32 xticks;
+
+ tmp = S390_lowcore.jiffy_timer - xtime_cc;
+ if (tmp >= 2*CLK_TICKS_PER_JIFFY) {
+ xticks = __calculate_ticks(tmp);
+ xtime_cc += (__u64) xticks*CLK_TICKS_PER_JIFFY;
+ } else {
+ xticks = 1;
+ xtime_cc += CLK_TICKS_PER_JIFFY;
+ }
+ while (xticks--)
+ do_timer(regs);
+ }
+ write_sequnlock(&xtime_lock);
+ while (ticks--)
+ update_process_times(user_mode(regs));
+#else
+ while (ticks--)
+ do_timer(regs);
+#endif
+ }
+ cpu_clear(smp_processor_id(), idle_cpu_mask);
+}
+
+/*
+ * Stop the HZ tick on the current CPU.
+ * Only cpu_idle may call this function.
+ */
+int stop_hz_timer(void)
+{
+ __u64 timer;
+
+ if (sysctl_hz_timer != 0)
+ return 1;
+
+ /*
+ * Leave the clock comparator set up for the next timer
+ * tick if either rcu or a softirq is pending.
+ */
+ if (rcu_pending(smp_processor_id()) || local_softirq_pending())
+ return 1;
+
+ /*
+ * This cpu is going really idle. Set up the clock comparator
+ * for the next event.
+ */
+ cpu_set(smp_processor_id(), idle_cpu_mask);
+ timer = (__u64) (next_timer_interrupt() - jiffies) + jiffies_64;
+ timer = jiffies_timer_cc + timer * CLK_TICKS_PER_JIFFY;
+ asm volatile ("SCKC %0" : : "m" (timer));
+
+ return 0;
+}
+#endif
+
+#if defined(CONFIG_VIRT_TIMER) || defined(CONFIG_NO_IDLE_HZ)
+
+void do_monitor_call(struct pt_regs *regs, long interruption_code)
+{
+ /* disable monitor call class 0 */
+ __ctl_clear_bit(8, 15);
+
+#ifdef CONFIG_VIRT_TIMER
+ start_cpu_timer();
+#endif
+#ifdef CONFIG_NO_IDLE_HZ
+ start_hz_timer(regs);
+#endif
+}
+
+/*
+ * called from cpu_idle to stop any timers
+ * returns 1 if CPU should not be stopped
+ */
+int stop_timers(void)
+{
+#ifdef CONFIG_VIRT_TIMER
+ if (stop_cpu_timer())
+ return 1;
+#endif
+
+#ifdef CONFIG_NO_IDLE_HZ
+ if (stop_hz_timer())
+ return 1;
+#endif
+
+ /* enable monitor call class 0 */
+ __ctl_set_bit(8, 15);
+
+ return 0;
+}
+
+#endif
+
/*
* Start the clock comparator and the virtual CPU timer
* on the current CPU.
diff -urN linux-2.6/arch/s390/kernel/traps.c linux-2.6-s390/arch/s390/kernel/traps.c
--- linux-2.6/arch/s390/kernel/traps.c Sun Apr 4 05:36:55 2004
+++ linux-2.6-s390/arch/s390/kernel/traps.c Wed Apr 21 20:25:33 2004
@@ -64,7 +64,7 @@
extern void pfault_interrupt(struct pt_regs *regs, __u16 error_code);
static ext_int_info_t ext_int_pfault;
#endif
-#ifdef CONFIG_VIRT_TIMER
+#if defined(CONFIG_NO_IDLE_HZ) || defined(CONFIG_VIRT_TIMER)
extern pgm_check_handler_t do_monitor_call;
#endif

@@ -631,7 +631,7 @@
#endif /* CONFIG_ARCH_S390X */
pgm_check_table[0x15] = &operand_exception;
pgm_check_table[0x1C] = &privileged_op;
-#ifdef CONFIG_VIRT_TIMER
+#if defined(CONFIG_VIRT_TIMER) || defined(CONFIG_NO_IDLE_HZ)
pgm_check_table[0x40] = &do_monitor_call;
#endif
if (MACHINE_IS_VM) {
diff -urN linux-2.6/include/asm-s390/cpumask.h linux-2.6-s390/include/asm-s390/cpumask.h
--- linux-2.6/include/asm-s390/cpumask.h Sun Apr 4 05:38:13 2004
+++ linux-2.6-s390/include/asm-s390/cpumask.h Wed Apr 21 20:23:48 2004
@@ -3,4 +3,7 @@

#include <asm-generic/cpumask.h>

+#define __ARCH_HAS_IDLE_CPU_MASK
+extern cpumask_t idle_cpu_mask;
+
#endif /* _ASM_S390_CPUMASK_H */
diff -urN linux-2.6/include/linux/sysctl.h linux-2.6-s390/include/linux/sysctl.h
--- linux-2.6/include/linux/sysctl.h Wed Apr 21 20:25:09 2004
+++ linux-2.6-s390/include/linux/sysctl.h Wed Apr 21 20:25:33 2004
@@ -132,6 +132,7 @@
KERN_PTY=62, /* dir: pty driver */
KERN_NGROUPS_MAX=63, /* int: NGROUPS_MAX */
KERN_SPARC_SCONS_PWROFF=64, /* int: serial console power-off halt */
+ KERN_HZ_TIMER=65, /* int: hz timer on or off */
};


diff -urN linux-2.6/include/linux/timer.h linux-2.6-s390/include/linux/timer.h
--- linux-2.6/include/linux/timer.h Sun Apr 4 05:37:37 2004
+++ linux-2.6-s390/include/linux/timer.h Wed Apr 21 20:25:33 2004
@@ -65,6 +65,8 @@
extern int __mod_timer(struct timer_list *timer, unsigned long expires);
extern int mod_timer(struct timer_list *timer, unsigned long expires);

+extern unsigned long next_timer_interrupt(void);
+
/***
* add_timer - start a timer
* @timer: the timer to be added
diff -urN linux-2.6/kernel/rcupdate.c linux-2.6-s390/kernel/rcupdate.c
--- linux-2.6/kernel/rcupdate.c Wed Apr 21 20:25:10 2004
+++ linux-2.6-s390/kernel/rcupdate.c Wed Apr 21 20:25:33 2004
@@ -96,6 +96,10 @@
}
}

+#ifndef __ARCH_HAS_IDLE_CPU_MASK
+#define idle_cpu_mask CPU_MASK_NONE
+#endif
+
/*
* Register a new batch of callbacks, and start it up if there is currently no
* active batch and the batch to be registered has not already occurred.
@@ -111,7 +115,10 @@
return;
}
/* Can't change, since spin lock held. */
- rcu_ctrlblk.rcu_cpu_mask = cpu_online_map;
+ rcu_ctrlblk.rcu_cpu_mask = idle_cpu_mask;
+ cpus_complement(rcu_ctrlblk.rcu_cpu_mask);
+ cpus_and(rcu_ctrlblk.rcu_cpu_mask, cpu_online_map,
+ rcu_ctrlblk.rcu_cpu_mask);
}

/*
diff -urN linux-2.6/kernel/sysctl.c linux-2.6-s390/kernel/sysctl.c
--- linux-2.6/kernel/sysctl.c Wed Apr 21 20:25:10 2004
+++ linux-2.6-s390/kernel/sysctl.c Wed Apr 21 20:25:33 2004
@@ -108,6 +108,8 @@
extern int sysctl_userprocess_debug;
#endif

+extern int sysctl_hz_timer;
+
#if defined(CONFIG_PPC32) && defined(CONFIG_6xx)
extern unsigned long powersave_nap;
int proc_dol2crvec(ctl_table *table, int write, struct file *filp,
@@ -573,6 +575,16 @@
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+#endif
+#ifdef CONFIG_NO_IDLE_HZ
+ {
+ .ctl_name = KERN_HZ_TIMER,
+ .procname = "hz_timer",
+ .data = &sysctl_hz_timer,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
#endif
{
.ctl_name = KERN_S390_USER_DEBUG_LOGGING,
diff -urN linux-2.6/kernel/timer.c linux-2.6-s390/kernel/timer.c
--- linux-2.6/kernel/timer.c Wed Apr 21 20:25:10 2004
+++ linux-2.6-s390/kernel/timer.c Wed Apr 21 20:25:33 2004
@@ -428,6 +428,75 @@
spin_unlock_irq(&base->lock);
}

+#ifdef CONFIG_NO_IDLE_HZ
+/*
+ * Find out when the next timer event is due to happen. This
+ * is used on S/390 to stop all activity when a cpus is idle.
+ * This functions needs to be called disabled.
+ */
+unsigned long next_timer_interrupt(void)
+{
+ tvec_base_t *base;
+ struct list_head *list;
+ struct timer_list *nte;
+ unsigned long expires;
+ tvec_t *varray[4];
+ int i, j;
+
+ base = &__get_cpu_var(tvec_bases);
+ spin_lock(&base->lock);
+ expires = base->timer_jiffies + (LONG_MAX >> 1);
+ list = 0;
+
+ /* Look for timer events in tv1. */
+ j = base->timer_jiffies & TVR_MASK;
+ do {
+ list_for_each_entry(nte, base->tv1.vec + j, entry) {
+ expires = nte->expires;
+ if (j < (base->timer_jiffies & TVR_MASK))
+ list = base->tv2.vec + (INDEX(0));
+ goto found;
+ }
+ j = (j + 1) & TVR_MASK;
+ } while (j != (base->timer_jiffies & TVR_MASK));
+
+ /* Check tv2-tv5. */
+ varray[0] = &base->tv2;
+ varray[1] = &base->tv3;
+ varray[2] = &base->tv4;
+ varray[3] = &base->tv5;
+ for (i = 0; i < 4; i++) {
+ j = INDEX(i);
+ do {
+ if (list_empty(varray[i]->vec + j)) {
+ j = (j + 1) & TVN_MASK;
+ continue;
+ }
+ list_for_each_entry(nte, varray[i]->vec + j, entry)
+ if (time_before(nte->expires, expires))
+ expires = nte->expires;
+ if (j < (INDEX(i)) && i < 3)
+ list = varray[i + 1]->vec + (INDEX(i + 1));
+ goto found;
+ } while (j != (INDEX(i)));
+ }
+found:
+ if (list) {
+ /*
+ * The search wrapped. We need to look at the next list
+ * from next tv element that would cascade into tv element
+ * where we found the timer element.
+ */
+ list_for_each_entry(nte, list, entry) {
+ if (time_before(nte->expires, expires))
+ expires = nte->expires;
+ }
+ }
+ spin_unlock(&base->lock);
+ return expires;
+}
+#endif
+
/******************************************************************/

/*
-
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