defbb2c929
The original ia64 udelay() was simple, but flawed for platforms without synchronized ITCs: a preemption and migration to another CPU during the while-loop likely resulted in too-early termination or very, very lengthy looping. The first fix (now in 2.6.15) broke the delay loop into smaller, non-preemptible chunks, reenabling preemption between the chunks. This fix is flawed in that the total udelay is computed to be the sum of just the non-premptible while-loop pieces, i.e., not counting the time spent in the interim preemptible periods. If an interrupt or a migration occurs during one of these interim periods, then that time is invisible and only serves to lengthen the effective udelay(). This new fix backs out the current flawed fix and returns to a simple udelay(), fully preemptible and interruptible. It implements two simple alternative udelay() routines: one a default generic version that uses ia64_get_itc(), and the other an sn-specific version that uses that platform's RTC. Signed-off-by: John Hawkes <hawkes@sgi.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
56 lines
1.3 KiB
C
56 lines
1.3 KiB
C
/*
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* linux/arch/ia64/sn/kernel/sn2/timer.c
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*
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* Copyright (C) 2003 Silicon Graphics, Inc.
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* Copyright (C) 2003 Hewlett-Packard Co
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* David Mosberger <davidm@hpl.hp.com>: updated for new timer-interpolation infrastructure
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*/
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/time.h>
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#include <linux/interrupt.h>
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#include <asm/hw_irq.h>
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#include <asm/system.h>
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#include <asm/timex.h>
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#include <asm/sn/leds.h>
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#include <asm/sn/shub_mmr.h>
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#include <asm/sn/clksupport.h>
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extern unsigned long sn_rtc_cycles_per_second;
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static struct time_interpolator sn2_interpolator = {
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.drift = -1,
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.shift = 10,
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.mask = (1LL << 55) - 1,
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.source = TIME_SOURCE_MMIO64
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};
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/*
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* sn udelay uses the RTC instead of the ITC because the ITC is not
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* synchronized across all CPUs, and the thread may migrate to another CPU
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* if preemption is enabled.
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*/
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static void
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ia64_sn_udelay (unsigned long usecs)
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{
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unsigned long start = rtc_time();
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unsigned long end = start +
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usecs * sn_rtc_cycles_per_second / 1000000;
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while (time_before((unsigned long)rtc_time(), end))
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cpu_relax();
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}
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void __init sn_timer_init(void)
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{
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sn2_interpolator.frequency = sn_rtc_cycles_per_second;
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sn2_interpolator.addr = RTC_COUNTER_ADDR;
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register_time_interpolator(&sn2_interpolator);
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ia64_udelay = &ia64_sn_udelay;
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}
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