* [Linux-ia64] Re: gettimeoffset() for sn2
2003-04-23 18:02 [Linux-ia64] Re: gettimeoffset() for sn2 David Mosberger
@ 2003-04-23 22:08 ` Jes Sorensen
2003-04-28 18:30 ` David Mosberger
1 sibling, 0 replies; 3+ messages in thread
From: Jes Sorensen @ 2003-04-23 22:08 UTC (permalink / raw)
To: linux-ia64
>>>>> "David" = David Mosberger <davidm@napali.hpl.hp.com> writes:
>>>>> On Wed, 23 Apr 2003 12:19:25 -0400, Jes Sorensen <jes@wildopensource.com> said:
Jes> This patch is against 2.4.21-pre5-cset-1.1020, I will be working
Jes> on a 2.5.x version later today.
Jes> Unless there are strong objections, I'd love to see this applied
Jes> to the 2.4.x tree. Oh yes, I tested it on my zx1 as well.
David> One small comment: lose the " = NULL" initializers for the
David> global *time_hook variables; they only increase the data size
David> for no good reason.
Whoops, good point, thanks.
David> The bigger issue: note that do_gettimeofday() acquires a _read_
David> lock. Thus, you need to be careful about updating rtc_offset
David> atomically.
Argh, you are right, here we go again, now I think I got it all
covered. However I think I will stop declaring victory on this one,
everytime I do so it comes back to haunt me. This version also fixed a
bug where i was scaling the RTC clock twice, not that it was lethal,
but it was still a bug.
Thanks for your comments.
Cheers,
Jes
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/arch/ia64/kernel/time.c linux-2.4.21-pre5-timer2/arch/ia64/kernel/time.c
--- linux-2.4.21-pre5-cset-1.1020/arch/ia64/kernel/time.c Thu Nov 28 18:53:09 2002
+++ linux-2.4.21-pre5-timer2/arch/ia64/kernel/time.c Wed Apr 23 11:48:58 2003
@@ -26,6 +26,9 @@
extern rwlock_t xtime_lock;
extern unsigned long wall_jiffies;
extern unsigned long last_time_offset;
+static unsigned long __ia64_gettimeoffset (void);
+
+unsigned long (*gettimeoffset)(void) = &__ia64_gettimeoffset;
#ifdef CONFIG_IA64_DEBUG_IRQ
@@ -33,6 +36,8 @@
#endif
+#define TIME_KEEPER_ID 0 /* smp_processor_id() of time-keeper */
+
static void
do_profile (unsigned long ip)
{
@@ -58,18 +63,18 @@
}
/*
- * Return the number of micro-seconds that elapsed since the last update to jiffy. The
- * xtime_lock must be at least read-locked when calling this routine.
+ * Return the number of micro-seconds that elapsed since the last update to
+ * jiffy. The xtime_lock must be at least read-locked when calling this
+ * routine.
*/
-static inline unsigned long
-gettimeoffset (void)
+static unsigned long
+__ia64_gettimeoffset (void)
{
unsigned long elapsed_cycles, lost = jiffies - wall_jiffies;
unsigned long now, last_tick;
-# define time_keeper_id 0 /* smp_processor_id() of time-keeper */
- last_tick = (cpu_data(time_keeper_id)->itm_next
- - (lost + 1)*cpu_data(time_keeper_id)->itm_delta);
+ last_tick = (cpu_data(TIME_KEEPER_ID)->itm_next
+ - (lost + 1)*cpu_data(TIME_KEEPER_ID)->itm_delta);
now = ia64_get_itc();
if ((long) (now - last_tick) < 0) {
@@ -102,6 +107,9 @@
tv->tv_sec--;
}
+ if (update_wall_time_hook)
+ update_wall_time_hook();
+
xtime = *tv;
time_adjust = 0; /* stop active adjtime() */
time_status |= STA_UNSYNC;
@@ -171,7 +179,7 @@
#endif
new_itm += local_cpu_data->itm_delta;
- if (smp_processor_id() = 0) {
+ if (smp_processor_id() = TIME_KEEPER_ID) {
/*
* Here we are in the timer irq handler. We have irqs locally
* disabled, but we don't know if the timer_bh is running on
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/arch/ia64/sn/kernel/setup.c linux-2.4.21-pre5-timer2/arch/ia64/sn/kernel/setup.c
--- linux-2.4.21-pre5-cset-1.1020/arch/ia64/sn/kernel/setup.c Sun Apr 6 17:14:59 2003
+++ linux-2.4.21-pre5-timer2/arch/ia64/sn/kernel/setup.c Wed Apr 23 11:36:26 2003
@@ -78,7 +78,6 @@
extern void bte_init_cpu (void);
unsigned long sn_rtc_cycles_per_second;
-unsigned long sn_rtc_usec_per_cyc;
partid_t sn_partid = -1;
char sn_system_serial_number_string[128];
@@ -209,6 +208,8 @@
extern nasid_t master_nasid;
+extern void sn_timer_init(void);
+
/**
* sn_setup - SN platform setup routine
* @cmdline_p: kernel command line
@@ -261,13 +262,6 @@
else
sn_rtc_cycles_per_second = ticks_per_sec;
-#ifdef CONFIG_IA64_SGI_SN1
- /* PROM has wrong value on SN1 */
- sn_rtc_cycles_per_second = 990177;
-#endif
- sn_rtc_usec_per_cyc = ((1000000UL<<IA64_USEC_PER_CYC_SHIFT)
- + sn_rtc_cycles_per_second/2) / sn_rtc_cycles_per_second;
-
for (i=0;i<NR_CPUS;i++)
_sn_irq_desc[i] = _irq_desc;
@@ -309,6 +303,8 @@
#endif
screen_info = sn_screen_info;
+ sn_timer_init();
+
/*
* Turn off "floating-point assist fault" warnings by default.
*/
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/arch/ia64/sn/kernel/sn2/Makefile linux-2.4.21-pre5-timer2/arch/ia64/sn/kernel/sn2/Makefile
--- linux-2.4.21-pre5-cset-1.1020/arch/ia64/sn/kernel/sn2/Makefile Sun Apr 6 17:14:59 2003
+++ linux-2.4.21-pre5-timer2/arch/ia64/sn/kernel/sn2/Makefile Wed Apr 23 11:37:01 2003
@@ -42,6 +42,7 @@
O_TARGET = sn2.o
-obj-y = cache.o iomv.o ptc_deadlock.o sn2_smp.o sn_proc_fs.o
+obj-y = cache.o iomv.o ptc_deadlock.o sn2_smp.o sn_proc_fs.o \
+ timer.o
include $(TOPDIR)/Rules.make
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/arch/ia64/sn/kernel/sn2/timer.c linux-2.4.21-pre5-timer2/arch/ia64/sn/kernel/sn2/timer.c
--- linux-2.4.21-pre5-cset-1.1020/arch/ia64/sn/kernel/sn2/timer.c Wed Dec 31 19:00:00 1969
+++ linux-2.4.21-pre5-timer2/arch/ia64/sn/kernel/sn2/timer.c Wed Apr 23 17:46:48 2003
@@ -0,0 +1,100 @@
+/*
+ * linux/arch/ia64/sn/kernel/sn2/timer.c
+ *
+ * Copyright (C) 2003 Silicon Graphics, Inc.
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/time.h>
+#include <linux/interrupt.h>
+
+#include <asm/hw_irq.h>
+#include <asm/system.h>
+
+#include <asm/sn/leds.h>
+#include <asm/sn/clksupport.h>
+
+
+extern unsigned long sn_rtc_cycles_per_second;
+static volatile unsigned long last_wall_rtc;
+
+/**
+ * gettimeoffset - number of usecs elapsed since &xtime was last updated
+ *
+ * This function is used by do_gettimeofday() to determine the number
+ * of usecs that have elapsed since the last update to &xtime. On SN
+ * this is accomplished using the RTC built in to each Hub chip; each
+ * is guaranteed to be synchronized by the PROM, so a local read will
+ * suffice (GET_RTC_COUNTER() does this for us). A snapshot of the RTC
+ * value is taken every time wall_jiffies is updated by the
+ * update_wall_time_hook (sn2_update_wall_time) which means we don't
+ * have to adjust for lost jiffies ticks or anything like that.
+ */
+extern unsigned long wall_jiffies; /* from kernel/timer.c */
+
+static volatile long rtc_offset;
+static long rtc_cycles_per_usec;
+static long rtc_per_timer_tick;
+
+unsigned long
+sn_gettimeoffset(void)
+{
+ long current_rtc, elapsed_rtc, old, new_offset;
+
+ do {
+ old = rtc_offset;
+ current_rtc = GET_RTC_COUNTER();
+
+ /*
+ * Need to address wrapping here!
+ */
+ elapsed_rtc = (long)(current_rtc - last_wall_rtc);
+
+ /*
+ * This case is non lethal as the max() will take care of it.
+ */
+#if 0
+ if (elapsed_rtc < 0) {
+ printk(KERN_ERR "sn_gettimeoffset(): time goes "
+ "backwards!\n current_rtc 0x%016lx, "
+ "last_wall_rtc 0x%016lx, elapsed %08lx, "
+ "offset %li\n", current_rtc, last_wall_rtc,
+ elapsed_rtc, max(elapsed_rtc, rtc_offset)/
+ rtc_cycles_per_usec);
+ }
+#endif
+
+ new_offset = max(elapsed_rtc, old);
+ } while (cmpxchg(&rtc_offset, old, new_offset) != old);
+
+ return new_offset / rtc_cycles_per_usec;
+}
+
+
+void sn2_update_wall_time(void)
+{
+ rtc_offset -= min(rtc_offset, rtc_per_timer_tick);
+ last_wall_rtc = GET_RTC_COUNTER();
+}
+
+
+void sn2_reset_wall_time(void)
+{
+ rtc_offset = 0;
+ last_wall_rtc = GET_RTC_COUNTER();
+}
+
+
+void __init
+sn_timer_init(void)
+{
+ rtc_per_timer_tick = sn_rtc_cycles_per_second / HZ;
+ rtc_cycles_per_usec = sn_rtc_cycles_per_second / 1000000;
+
+ last_wall_rtc = GET_RTC_COUNTER();
+ update_wall_time_hook = sn2_update_wall_time;
+ reset_wall_time_hook = sn2_reset_wall_time;
+ gettimeoffset = sn_gettimeoffset;
+}
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/include/asm-ia64/sn/clksupport.h linux-2.4.21-pre5-timer2/include/asm-ia64/sn/clksupport.h
--- linux-2.4.21-pre5-cset-1.1020/include/asm-ia64/sn/clksupport.h Sun Apr 6 17:15:02 2003
+++ linux-2.4.21-pre5-timer2/include/asm-ia64/sn/clksupport.h Wed Apr 23 11:25:48 2003
@@ -38,7 +38,7 @@
extern nasid_t master_nasid;
-#define RTC_MASK (0x007fffffffffffff)
+#define RTC_MASK 0x007fffffffffffffUL
/* clocks are not synchronized yet on SN1 - used node 0 (problem if no NASID 0) */
#define RTC_COUNTER_ADDR ((clkreg_t*)REMOTE_HUB_ADDR(master_nasid, PI_RT_COUNTER))
#define RTC_COMPARE_A_ADDR ((clkreg_t*)REMOTE_HUB_ADDR(master_nasid, PI_RT_COMPARE_A))
@@ -52,7 +52,7 @@
#include <asm/sn/sn2/addrs.h>
#include <asm/sn/sn2/shubio.h>
#include <asm/sn/sn2/shub_mmr.h>
-#define RTC_MASK (SH_RTC_MASK)
+#define RTC_MASK SH_RTC_MASK
#define RTC_COUNTER_ADDR ((clkreg_t*)LOCAL_MMR_ADDR(SH_RTC))
#define RTC_COMPARE_A_ADDR ((clkreg_t*)LOCAL_MMR_ADDR(SH_RTC))
#define RTC_COMPARE_B_ADDR ((clkreg_t*)LOCAL_MMR_ADDR(SH_RTC))
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/include/linux/timex.h linux-2.4.21-pre5-timer2/include/linux/timex.h
--- linux-2.4.21-pre5-cset-1.1020/include/linux/timex.h Sun Apr 6 17:37:58 2003
+++ linux-2.4.21-pre5-timer2/include/linux/timex.h Wed Apr 23 11:25:55 2003
@@ -286,6 +286,13 @@
extern long pps_errcnt; /* calibration errors */
extern long pps_stbcnt; /* stability limit exceeded */
+/*
+ * Call-back for high precision timer sources to snapshot every time
+ * wall_jiffies is updated.
+ */
+extern void (*update_wall_time_hook)(void);
+extern void (*reset_wall_time_hook)(void);
+
#endif /* KERNEL */
#endif /* LINUX_TIMEX_H */
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/kernel/time.c linux-2.4.21-pre5-timer2/kernel/time.c
--- linux-2.4.21-pre5-cset-1.1020/kernel/time.c Sun Apr 6 17:17:16 2003
+++ linux-2.4.21-pre5-timer2/kernel/time.c Wed Apr 23 11:25:55 2003
@@ -82,6 +82,9 @@
return -EFAULT;
write_lock_irq(&xtime_lock);
vxtime_lock();
+
+ if (reset_wall_time_hook)
+ reset_wall_time_hook();
xtime.tv_sec = value;
xtime.tv_usec = 0;
vxtime_unlock();
diff -urN -X /home/jes/exclude-linux linux-2.4.21-pre5-cset-1.1020/kernel/timer.c linux-2.4.21-pre5-timer2/kernel/timer.c
--- linux-2.4.21-pre5-cset-1.1020/kernel/timer.c Sun Apr 6 17:17:16 2003
+++ linux-2.4.21-pre5-timer2/kernel/timer.c Wed Apr 23 16:13:45 2003
@@ -514,6 +514,15 @@
}
/*
+ * Hook for using external high precision timers for the system clock.
+ * On systems where the CPU clock isn't synchronized between CPUs,
+ * it is necessary to use an external source such as an RTC to obtain
+ * precision in gettimeofday().
+ */
+void (*update_wall_time_hook)(void);
+void (*reset_wall_time_hook)(void);
+
+/*
* Using a loop looks inefficient, but "ticks" is
* usually just one (we shouldn't be losing ticks,
* we're doing this this way mainly for interrupt
@@ -525,12 +534,17 @@
do {
ticks--;
update_wall_time_one_tick();
+
+ if (update_wall_time_hook)
+ update_wall_time_hook();
} while (ticks);
if (xtime.tv_usec >= 1000000) {
xtime.tv_usec -= 1000000;
xtime.tv_sec++;
second_overflow();
+ if (update_wall_time_hook)
+ update_wall_time_hook();
}
}
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