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SubjectRe: [RFC][PATCH] linux-2.5.64_monotonic-clock_A0
john stultz wrote:
> All,
> Recently I've been working with Joel Becker, author of the
> hangcheck-timer code (already accepted into 2.5) to resolve issues when
> running his code on systems without synced TSCs.
>
> The basic problem is that the hangcheck-timer code (Required for Oracle)
> needs a accurate hard clock which can be used to detect OS stalls (due
> to udelay() or pci bus hangs) that would cause system time to skew (its
> sort of a sanity check that insures the system's notion of time is
> accurate). However, currently they are using get_cycles() to fetch the
> cpu's TSC register, thus this does not work on systems w/o a synced TSC.
> As suggested by Andi Kleen (see thread here:
> http://www.uwsg.iu.edu/hypermail/linux/kernel/0302.0/1234.html ) I've
> worked with Joel and others to implement the monotonic_clock()
> interface.
>
> This interface returns a unsigned long long representing the number of
> nanoseconds that has passed since time_init().
>
> Since we're dealing with 64bit values the cost of the math required to
> do the cycles->ns conversion is a big concern. I'd be very happy if
> someone could suggest a faster way.

IMHO I solved this problem in the high-res timers patch. I have
posted the core of the conversion stuff as a path (last night at
23:24) with this subject "[PATCH] Functions to do easy scaled math."
It consists of a header file containing a handful of inline asm code
to do the messy stuff (i.e. the stuff C can't do due to standard
restrictions). I also provided an asm-generic version to fill the gap
on other archs. Oh, and there is even a text file to explain it all.

-g

>
> Future plans to the interface include properly handling cpu_freq changes
> and porting to the different arches.
>
> Comments and suggestions requested, flames expected :)
>
> thanks
> -john
>
> diff -Nru a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
> --- a/arch/i386/kernel/time.c Thu Mar 6 16:12:27 2003
> +++ b/arch/i386/kernel/time.c Thu Mar 6 16:12:27 2003
> @@ -138,6 +138,19 @@
> clock_was_set();
> }
>
> +unsigned long long monotonic_clock(void)
> +{
> + unsigned long long ret;
> + unsigned long seq;
> + do {
> + seq = read_seqbegin(&xtime_lock);
> + ret = timer->monotonic_clock();
> + } while (read_seqretry(&xtime_lock, seq));
> + return ret;
> +}
> +EXPORT_SYMBOL(monotonic_clock);
> +
> +
> /*
> * In order to set the CMOS clock precisely, set_rtc_mmss has to be
> * called 500 ms after the second nowtime has started, because when
> diff -Nru a/arch/i386/kernel/timers/timer_cyclone.c b/arch/i386/kernel/timers/timer_cyclone.c
> --- a/arch/i386/kernel/timers/timer_cyclone.c Thu Mar 6 16:12:27 2003
> +++ b/arch/i386/kernel/timers/timer_cyclone.c Thu Mar 6 16:12:27 2003
> @@ -27,19 +27,24 @@
> #define CYCLONE_MPMC_OFFSET 0x51D0
> #define CYCLONE_MPCS_OFFSET 0x51A8
> #define CYCLONE_TIMER_FREQ 100000000
> -
> +#define CYCLONE_TIMER_MASK (((u64)1<<40)-1) /*40 bit mask*/
> int use_cyclone = 0;
>
> static u32* volatile cyclone_timer; /* Cyclone MPMC0 register */
> -static u32 last_cyclone_timer;
> +static u32 last_cyclone_low;
> +static u32 last_cyclone_high;
> +static unsigned long long monotonic_base;
>
> static void mark_offset_cyclone(void)
> {
> int count;
> + unsigned long long this_offset, last_offset;
> + last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
> +
> spin_lock(&i8253_lock);
> /* quickly read the cyclone timer */
> - if(cyclone_timer)
> - last_cyclone_timer = cyclone_timer[0];
> + last_cyclone_high = cyclone_timer[1];
> + last_cyclone_low = cyclone_timer[0];
>
> /* calculate delay_at_last_interrupt */
> outb_p(0x00, 0x43); /* latch the count ASAP */
> @@ -50,6 +55,10 @@
>
> count = ((LATCH-1) - count) * TICK_SIZE;
> delay_at_last_interrupt = (count + LATCH/2) / LATCH;
> +
> + /* update the monotonic base value */
> + this_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
> + monotonic_base += (this_offset - last_offset) & CYCLONE_TIMER_MASK;
> }
>
> static unsigned long get_offset_cyclone(void)
> @@ -63,7 +72,7 @@
> offset = cyclone_timer[0];
>
> /* .. relative to previous jiffy */
> - offset = offset - last_cyclone_timer;
> + offset = offset - last_cyclone_low;
>
> /* convert cyclone ticks to microseconds */
> /* XXX slow, can we speed this up? */
> @@ -73,6 +82,21 @@
> return delay_at_last_interrupt + offset;
> }
>
> +static unsigned long long monotonic_clock_cyclone(void)
> +{
> +
> + u32 now_low = cyclone_timer[0];
> + u32 now_high = cyclone_timer[1];
> + unsigned long long last_offset, this_offset;
> + unsigned long long ret;
> + last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
> + this_offset = ((unsigned long long)now_high<<32)|now_low;
> +
> + ret = monotonic_base + ((this_offset - last_offset)&CYCLONE_TIMER_MASK);
> + ret = ret * (1000000000 / CYCLONE_TIMER_FREQ);
> + return ret;
> +}
> +
> static int init_cyclone(void)
> {
> u32* reg;
> @@ -190,5 +214,6 @@
> .init = init_cyclone,
> .mark_offset = mark_offset_cyclone,
> .get_offset = get_offset_cyclone,
> + .monotonic_clock = monotonic_clock_cyclone,
> .delay = delay_cyclone,
> };
> diff -Nru a/arch/i386/kernel/timers/timer_none.c b/arch/i386/kernel/timers/timer_none.c
> --- a/arch/i386/kernel/timers/timer_none.c Thu Mar 6 16:12:27 2003
> +++ b/arch/i386/kernel/timers/timer_none.c Thu Mar 6 16:12:27 2003
> @@ -15,6 +15,11 @@
> return 0;
> }
>
> +static unsigned long long monotonic_clock_none(void)
> +{
> + return 0;
> +}
> +
> static void delay_none(unsigned long loops)
> {
> int d0;
> @@ -33,5 +38,6 @@
> .init = init_none,
> .mark_offset = mark_offset_none,
> .get_offset = get_offset_none,
> + .monotonic_clock = monotonic_clock_none,
> .delay = delay_none,
> };
> diff -Nru a/arch/i386/kernel/timers/timer_pit.c b/arch/i386/kernel/timers/timer_pit.c
> --- a/arch/i386/kernel/timers/timer_pit.c Thu Mar 6 16:12:27 2003
> +++ b/arch/i386/kernel/timers/timer_pit.c Thu Mar 6 16:12:27 2003
> @@ -27,6 +27,11 @@
> /* nothing needed */
> }
>
> +static unsigned long long monotonic_clock_pit(void)
> +{
> + return 0;
> +}
> +
> static void delay_pit(unsigned long loops)
> {
> int d0;
> @@ -141,5 +146,6 @@
> .init = init_pit,
> .mark_offset = mark_offset_pit,
> .get_offset = get_offset_pit,
> + .monotonic_clock = monotonic_clock_pit,
> .delay = delay_pit,
> };
> diff -Nru a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
> --- a/arch/i386/kernel/timers/timer_tsc.c Thu Mar 6 16:12:27 2003
> +++ b/arch/i386/kernel/timers/timer_tsc.c Thu Mar 6 16:12:27 2003
> @@ -23,6 +23,45 @@
> static int delay_at_last_interrupt;
>
> static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
> +static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
> +static unsigned long long monotonic_base;
> +
> +
> +/*
> + * accurate 64-bit/32-bit division, stolen from smpboot.c
> + */
> +unsigned long long div64 (unsigned long long a, unsigned long b0)
> +{
> + unsigned int a1, a2;
> + unsigned long long res;
> +
> + a1 = ((unsigned int*)&a)[0];
> + a2 = ((unsigned int*)&a)[1];
> +
> + res = a1/b0 +
> + (unsigned long long)a2 * (unsigned long long)(0xffffffff/b0) +
> + a2 / b0 +
> + (a2 * (0xffffffff % b0)) / b0;
> +
> + return res;
> +}
> +
> +static inline unsigned long long cycles_2_ns(unsigned long long cyc)
> +{
> + unsigned long long ret;
> + unsigned long cpu_mhz = cpu_khz/1000;
> +
> + /* convert from cycles(64bits) => nanoseconds (64bits)
> + * basic equation:
> + * cycles / ((cycles / sec) * (1sec / 10^9ns)) = ns
> + * cycles / ((cpu_mhz * 1000000) / 10^9)) = ns
> + * cycles / (cpu_mhz / 10^3) = ns
> + * cycles * 10^3 / cpu_mhz = ns
> + */
> + ret = cyc * 1000;
> + ret = div64(ret,cpu_mhz);
> + return ret;
> +}
>
> /* Cached *multiplier* to convert TSC counts to microseconds.
> * (see the equation below).
> @@ -60,11 +99,25 @@
> return delay_at_last_interrupt + edx;
> }
>
> +static unsigned long long monotonic_clock_tsc(void)
> +{
> + unsigned long long last_offset, this_offset;
> + last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
> +
> + /* Read the Time Stamp Counter */
> + rdtscll(this_offset);
> +
> + /* return the value in ns */
> + return monotonic_base + cycles_2_ns(this_offset - last_offset);
> +}
> +
> static void mark_offset_tsc(void)
> {
> int count;
> int countmp;
> static int count1=0, count2=LATCH;
> + unsigned long long this_offset, last_offset;
> + last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
> /*
> * It is important that these two operations happen almost at
> * the same time. We do the RDTSC stuff first, since it's
> @@ -79,7 +132,7 @@
>
> /* read Pentium cycle counter */
>
> - rdtscl(last_tsc_low);
> + rdtsc(last_tsc_low, last_tsc_high);
>
> spin_lock(&i8253_lock);
> outb_p(0x00, 0x43); /* latch the count ASAP */
> @@ -104,6 +157,11 @@
>
> count = ((LATCH-1) - count) * TICK_SIZE;
> delay_at_last_interrupt = (count + LATCH/2) / LATCH;
> +
> + /* update the monotonic base value */
> + this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
> + monotonic_base += cycles_2_ns(this_offset - last_offset);
> +
> }
>
> static void delay_tsc(unsigned long loops)
> @@ -326,5 +384,6 @@
> .init = init_tsc,
> .mark_offset = mark_offset_tsc,
> .get_offset = get_offset_tsc,
> + .monotonic_clock = monotonic_clock_tsc,
> .delay = delay_tsc,
> };
> diff -Nru a/drivers/char/hangcheck-timer.c b/drivers/char/hangcheck-timer.c
> --- a/drivers/char/hangcheck-timer.c Thu Mar 6 16:12:27 2003
> +++ b/drivers/char/hangcheck-timer.c Thu Mar 6 16:12:27 2003
> @@ -78,11 +78,13 @@
> static struct timer_list hangcheck_ticktock =
> TIMER_INITIALIZER(hangcheck_fire, 0, 0);
>
> +extern unsigned long long monotonic_clock(void);
> +
> static void hangcheck_fire(unsigned long data)
> {
> unsigned long long cur_tsc, tsc_diff;
>
> - cur_tsc = get_cycles();
> + cur_tsc = monotonic_clock();
>
> if (cur_tsc > hangcheck_tsc)
> tsc_diff = cur_tsc - hangcheck_tsc;
> @@ -98,7 +100,7 @@
> }
> }
> mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
> - hangcheck_tsc = get_cycles();
> + hangcheck_tsc = monotonic_clock();
> }
>
>
> @@ -108,10 +110,10 @@
> VERSION_STR, hangcheck_tick, hangcheck_margin);
>
> hangcheck_tsc_margin = hangcheck_margin + hangcheck_tick;
> - hangcheck_tsc_margin *= HZ;
> - hangcheck_tsc_margin *= current_cpu_data.loops_per_jiffy;
> + hangcheck_tsc_margin *= 1000000000;
> +
>
> - hangcheck_tsc = get_cycles();
> + hangcheck_tsc = monotonic_clock();
> mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));
>
> return 0;
> diff -Nru a/include/asm-i386/timer.h b/include/asm-i386/timer.h
> --- a/include/asm-i386/timer.h Thu Mar 6 16:12:27 2003
> +++ b/include/asm-i386/timer.h Thu Mar 6 16:12:27 2003
> @@ -14,6 +14,7 @@
> int (*init)(void);
> void (*mark_offset)(void);
> unsigned long (*get_offset)(void);
> + unsigned long long (*monotonic_clock)(void);
> void (*delay)(unsigned long);
> };
>
>
>

--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

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