Commit 8107d829 authored Nov 27, 2008 by Christian Borntraeger Committed by Martin Schwidefsky Nov 27, 2008

[S390] fix/cleanup sched_clock



CONFIG_PRINTK_TIME reveals that sched_clock has a wrong offset during boot:
..
[    0.000000]   Movable zone: 0 pages used for memmap
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 775679
[    0.000000] Kernel command line: dasd=4b6c root=/dev/dasda1 ro noinitrd
[    0.000000] PID hash table entries: 4096 (order: 12, 32768 bytes)
[6920575.975232] console [ttyS0] enabled
[6920575.987586] Dentry cache hash table entries: 524288 (order: 10, 4194304 bytes)
[6920575.991404] Inode-cache hash table entries: 262144 (order: 9, 2097152 bytes)
..

The s390 implementation of sched_clock uses the store clock instruction and
subtracts jiffies_timer_cc.
jiffies_timer_cc is a local variable in arch/s390/kernel/time.c and only used
for sched_clock and monotonic clock. For historical reasons there is an offset
on that value. With todays code this offset is unnecessary. By removing that
offset we can get a sched_clock which returns the nanoseconds after time_init.
This improves CONFIG_PRINTK_TIME.

Since sched_clock is the only user, I have also renamed jiffies_timer_cc to
sched_clock_base_cc. In addition, the local variable init_timer_cc is redundant
and can be romved as well.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 59da2139

arch/s390/kernel/time.c

+5 −8

Original line number	Diff line number	Diff line
		@@ -59,7 +59,7 @@

		static ext_int_info_t ext_int_info_cc;
		static ext_int_info_t ext_int_etr_cc;
		static u64 jiffies_timer_cc;
		static u64 sched_clock_base_cc;

		static DEFINE_PER_CPU(struct clock_event_device, comparators);

		@@ -68,7 +68,7 @@ static DEFINE_PER_CPU(struct clock_event_device, comparators);
		*/
		unsigned long long sched_clock(void)
		{
		return ((get_clock_xt() - jiffies_timer_cc) * 125) >> 9;
		return ((get_clock_xt() - sched_clock_base_cc) * 125) >> 9;
		}

		/*
		@@ -229,13 +229,10 @@ static struct clocksource clocksource_tod = {
		*/
		void __init time_init(void)
		{
		u64 init_timer_cc;

		init_timer_cc = reset_tod_clock();
		jiffies_timer_cc = init_timer_cc - jiffies_64 * CLK_TICKS_PER_JIFFY;
		sched_clock_base_cc = reset_tod_clock();

		/* set xtime */
		tod_to_timeval(init_timer_cc - TOD_UNIX_EPOCH, &xtime);
		tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, &xtime);
		set_normalized_timespec(&wall_to_monotonic,
		-xtime.tv_sec, -xtime.tv_nsec);

		@@ -289,7 +286,7 @@ static unsigned long long adjust_time(unsigned long long old,
		delta = -delta;
		adjust.offset = -ticks * (1000000 / HZ);
		}
		jiffies_timer_cc += delta;
		sched_clock_base_cc += delta;
		if (adjust.offset != 0) {
		printk(KERN_NOTICE "etr: time adjusted by %li micro-seconds\n",
		adjust.offset);

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