* Dave Johnson <djohnson+linuxmips@xxxxxxxxxxxxxxxxxxxxxx> [2005-07-20 10:43]:
> Below are 2 fixes I made to 2.6.12 to do with time jumping around
> as reported by gettimeofday(). One is SB1250 specific and one appears
> generic.
>
> The symptom is revealed by running multile copies (1 per cpu) of a
> simple test program that calls gettimeofday() as fast as possible
> looking for time to go backwards.
>
> When a jump is detected the program outputs a few samples before and
> after each jump:
Does anyone have comments regarding this patch?
> value delta
> 1121781527.912525: 1
> 1121781527.912525: 0
> 1121781527.912526: 1
> 1121781527.912526: 0
> 1121781527.912527: 1
> 1121781527.912527: 0
> 1121781527.912527: 0
> 1121781527.912527: 0
> 1121781527.911528: -999
> 1121781527.911529: 1
> 1121781527.911530: 1
> 1121781527.912532: 1002
> 1121781527.912533: 1
> 1121781527.912533: 0
> 1121781527.912534: 1
> 1121781527.912534: 0
> 1121781527.912535: 1
> 1121781527.912536: 1
>
> value delta
> 1121781545.635524: 1
> 1121781545.635524: 0
> 1121781545.635525: 1
> 1121781545.635525: 0
> 1121781545.635526: 1
> 1121781545.635526: 0
> 1121781545.635527: 1
> 1121781545.635527: 0
> 1121781545.634527: -1000
> 1121781545.635527: 1000
> 1121781545.635528: 1
> 1121781545.635529: 1
> 1121781545.635529: 0
> 1121781545.635530: 1
> 1121781545.635530: 0
> 1121781545.635531: 1
> 1121781545.635531: 0
> 1121781545.635532: 1
> 1121781545.635533: 1
>
> Time jumps backwards 1msec then forwards 1msec a few usec
> later. Usually lasts < 2us but I've seen it as long as 5us if the
> system is under load.
>
> --
>
> First problem I found is that sb1250_gettimeoffset() simply reads the
> current cpu 0 timer remaining value, however once this counter reaches
> 0 and the interrupt is raised, it immediately resets and begins to
> count down again.
>
> If sb1250_gettimeoffset() is called on cpu 1 via do_gettimeofday()
> after the timer has reset but prior to cpu 0 processing the interrupt
> and taking write_seqlock() in timer_interrupt() it will return a
> full value (or close to it) causing time to jump backwards 1ms. Once
> cpu 0 handles the interrupt and timer_interrupt() gets far enough
> along it will jump forward 1ms.
>
> To fix this problem I implemented mips_hpt_*() on sb1250 using a spare
> timer unrelated to the existing periodic interrupt timers. It runs at
> 1Mhz with a full 23bit counter. This eliminated the custom
> do_gettimeoffset() for sb1250 and allowed use of the generic
> fixed_rate_gettimeoffset() using mips_hpt_*() and timerhi/timerlo.
>
> --
>
> The second problem is that more of timer_interrupt() needs to be
> protected by xtime_lock:
>
> * do_timer() expects the arch-specific handler to take the lock as it
> modifies jiffies[_64] and xtime.
> * writing timerhi/lo in timer_interrupt() will mess up
> fixed_rate_gettimeoffset() which reads timerhi/lo.
>
> --
>
> With both changes do_gettimeofday() works correctly on both cpu 0 and
> cpu 1.
>
> --
>
> Other changes/cleanups:
>
> The existing sb1250 periodic timers were slow by 999ppm (given a
> perfect 100mhz reference). The timers need to be loaded with 1 less
> than the desired interval not the interval itself.
>
> M_SCD_TIMER_INIT and M_SCD_TIMER_CNT had the wrong field width (should
> be 23 bits not 20 bits)
>
> --
> Dave Johnson
> Starent Networks
>
> ============
>
> diff -Nru a/arch/mips/kernel/time.c b/arch/mips/kernel/time.c
> --- a/arch/mips/kernel/time.c 2005-07-20 10:25:22 -04:00
> +++ b/arch/mips/kernel/time.c 2005-07-20 10:25:22 -04:00
> @@ -424,6 +424,8 @@
> unsigned long j;
> unsigned int count;
>
> + write_seqlock(&xtime_lock);
> +
> count = mips_hpt_read();
> mips_timer_ack();
>
> @@ -441,7 +443,6 @@
> * CMOS clock accordingly every ~11 minutes. rtc_set_time() has to be
> * called as close as possible to 500 ms before the new second starts.
> */
> - write_seqlock(&xtime_lock);
> if ((time_status & STA_UNSYNC) == 0 &&
> xtime.tv_sec > last_rtc_update + 660 &&
> (xtime.tv_nsec / 1000) >= 500000 - ((unsigned) TICK_SIZE) / 2 &&
> @@ -453,7 +454,6 @@
> last_rtc_update = xtime.tv_sec - 600;
> }
> }
> - write_sequnlock(&xtime_lock);
>
> /*
> * If jiffies has overflown in this timer_interrupt, we must
> @@ -495,6 +495,8 @@
> break;
> }
> }
> +
> + write_sequnlock(&xtime_lock);
>
> /*
> * In UP mode, we call local_timer_interrupt() to do profiling
> diff -Nru a/arch/mips/sibyte/sb1250/time.c b/arch/mips/sibyte/sb1250/time.c
> --- a/arch/mips/sibyte/sb1250/time.c 2005-07-20 10:25:22 -04:00
> +++ b/arch/mips/sibyte/sb1250/time.c 2005-07-20 10:25:22 -04:00
> @@ -47,23 +47,51 @@
> #define IMR_IP3_VAL K_INT_MAP_I1
> #define IMR_IP4_VAL K_INT_MAP_I2
>
> +#define SB1250_HPT_NUM 3
> +#define SB1250_HPT_VALUE M_SCD_TIMER_CNT /* max value */
> +#define SB1250_HPT_SHIFT ((sizeof(unsigned int)*8)-V_SCD_TIMER_WIDTH)
> +
> +
> extern int sb1250_steal_irq(int irq);
>
> +static unsigned int sb1250_hpt_read(void);
> +static void sb1250_hpt_init(unsigned int);
> +
> +static unsigned int hpt_offset;
> +
> +void __init sb1250_hpt_setup(void)
> +{
> + int cpu = smp_processor_id();
> +
> + if (!cpu) {
> + /* Setup hpt using timer #3 but do not enable irq for it */
> + __raw_writeq(0, IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_CFG)));
> + __raw_writeq(SB1250_HPT_VALUE,
> + IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_INIT)));
> + __raw_writeq(M_SCD_TIMER_ENABLE | M_SCD_TIMER_MODE_CONTINUOUS,
> + IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_CFG)));
> +
> + /*
> + * we need to fill 32 bits, so just use the upper 23 bits and pretend
> + * the timer is going 512Mhz instead of 1Mhz
> + */
> + mips_hpt_frequency = V_SCD_TIMER_FREQ << SB1250_HPT_SHIFT;
> + mips_hpt_init = sb1250_hpt_init;
> + mips_hpt_read = sb1250_hpt_read;
> + }
> +}
> +
> +
> void sb1250_time_init(void)
> {
> int cpu = smp_processor_id();
> int irq = K_INT_TIMER_0+cpu;
>
> - /* Only have 4 general purpose timers */
> - if (cpu > 3) {
> + /* Only have 4 general purpose timers, and we use last one as hpt */
> + if (cpu > 2) {
> BUG();
> }
>
> - if (!cpu) {
> - /* Use our own gettimeoffset() routine */
> - do_gettimeoffset = sb1250_gettimeoffset;
> - }
> -
> sb1250_mask_irq(cpu, irq);
>
> /* Map the timer interrupt to ip[4] of this cpu */
> @@ -75,10 +103,10 @@
> /* Disable the timer and set up the count */
> __raw_writeq(0, IOADDR(A_SCD_TIMER_REGISTER(cpu, R_SCD_TIMER_CFG)));
> #ifdef CONFIG_SIMULATION
> - __raw_writeq(50000 / HZ,
> + __raw_writeq((50000 / HZ) - 1,
> IOADDR(A_SCD_TIMER_REGISTER(cpu, R_SCD_TIMER_INIT)));
> #else
> - __raw_writeq(1000000 / HZ,
> + __raw_writeq((V_SCD_TIMER_FREQ / HZ) - 1,
> IOADDR(A_SCD_TIMER_REGISTER(cpu, R_SCD_TIMER_INIT)));
> #endif
>
> @@ -104,7 +132,7 @@
> int cpu = smp_processor_id();
> int irq = K_INT_TIMER_0 + cpu;
>
> - /* Reset the timer */
> + /* ACK interrupt */
> ____raw_writeq(M_SCD_TIMER_ENABLE | M_SCD_TIMER_MODE_CONTINUOUS,
> IOADDR(A_SCD_TIMER_REGISTER(cpu, R_SCD_TIMER_CFG)));
>
> @@ -122,15 +150,26 @@
> }
>
> /*
> - * We use our own do_gettimeoffset() instead of the generic one,
> - * because the generic one does not work for SMP case.
> - * In addition, since we use general timer 0 for system time,
> - * we can get accurate intra-jiffy offset without calibration.
> + * The HPT is free running from SB1250_HPT_VALUE down to 0 then starts over
> + * again. There's no easy way to set to a specific value so store init value
> + * in hpt_offset and subtract each time.
> + *
> + * Note: Timer isn't full 32bits so shift it into the upper part making
> + * it appear to run at a higher frequency.
> */
> -unsigned long sb1250_gettimeoffset(void)
> +static unsigned int sb1250_hpt_read(void)
> {
> - unsigned long count =
> - __raw_readq(IOADDR(A_SCD_TIMER_REGISTER(0, R_SCD_TIMER_CNT)));
> + unsigned int count;
> +
> + count = G_SCD_TIMER_CNT(__raw_readq(IOADDR(A_SCD_TIMER_REGISTER(SB1250_HPT_NUM, R_SCD_TIMER_CNT))));
>
> - return 1000000/HZ - count;
> - }
> + count = (SB1250_HPT_VALUE - count) << SB1250_HPT_SHIFT;
> +
> + return count - hpt_offset;
> +}
> +
> +static void sb1250_hpt_init(unsigned int count)
> +{
> + hpt_offset = count;
> + return;
> +}
> diff -Nru a/arch/mips/sibyte/swarm/setup.c b/arch/mips/sibyte/swarm/setup.c
> --- a/arch/mips/sibyte/swarm/setup.c 2005-07-20 10:25:22 -04:00
> +++ b/arch/mips/sibyte/swarm/setup.c 2005-07-20 10:25:22 -04:00
> @@ -64,6 +64,12 @@
> return "SiByte " SIBYTE_BOARD_NAME;
> }
>
> +void __init swarm_time_init(void)
> +{
> + /* Setup HPT */
> + sb1250_hpt_setup();
> +}
> +
> void __init swarm_timer_setup(struct irqaction *irq)
> {
> /*
> @@ -96,6 +102,7 @@
>
> panic_timeout = 5; /* For debug. */
>
> + board_time_init = swarm_time_init;
> board_timer_setup = swarm_timer_setup;
> board_be_handler = swarm_be_handler;
>
> diff -Nru a/include/asm-mips/sibyte/sb1250.h b/include/asm-mips/sibyte/sb1250.h
> --- a/include/asm-mips/sibyte/sb1250.h 2005-07-20 10:25:22 -04:00
> +++ b/include/asm-mips/sibyte/sb1250.h 2005-07-20 10:25:22 -04:00
> @@ -41,8 +41,8 @@
> extern unsigned int periph_rev;
> extern unsigned int zbbus_mhz;
>
> +extern void sb1250_hpt_setup(void);
> extern void sb1250_time_init(void);
> -extern unsigned long sb1250_gettimeoffset(void);
> extern void sb1250_mask_irq(int cpu, int irq);
> extern void sb1250_unmask_irq(int cpu, int irq);
> extern void sb1250_smp_finish(void);
> diff -Nru a/include/asm-mips/sibyte/sb1250_scd.h b/include/asm-mips/sibyte/sb1250_scd.h
> --- a/include/asm-mips/sibyte/sb1250_scd.h 2005-07-20 10:25:22 -04:00
> +++ b/include/asm-mips/sibyte/sb1250_scd.h 2005-07-20 10:25:22 -04:00
> @@ -307,14 +307,15 @@
> */
>
> #define V_SCD_TIMER_FREQ 1000000
> +#define V_SCD_TIMER_WIDTH 23
>
> #define S_SCD_TIMER_INIT 0
> -#define M_SCD_TIMER_INIT _SB_MAKEMASK(20,S_SCD_TIMER_INIT)
> +#define M_SCD_TIMER_INIT _SB_MAKEMASK(V_SCD_TIMER_WIDTH,S_SCD_TIMER_INIT)
> #define V_SCD_TIMER_INIT(x) _SB_MAKEVALUE(x,S_SCD_TIMER_INIT)
> #define G_SCD_TIMER_INIT(x) _SB_GETVALUE(x,S_SCD_TIMER_INIT,M_SCD_TIMER_INIT)
>
> #define S_SCD_TIMER_CNT 0
> -#define M_SCD_TIMER_CNT _SB_MAKEMASK(20,S_SCD_TIMER_CNT)
> +#define M_SCD_TIMER_CNT _SB_MAKEMASK(V_SCD_TIMER_WIDTH,S_SCD_TIMER_CNT)
> #define V_SCD_TIMER_CNT(x) _SB_MAKEVALUE(x,S_SCD_TIMER_CNT)
> #define G_SCD_TIMER_CNT(x) _SB_GETVALUE(x,S_SCD_TIMER_CNT,M_SCD_TIMER_CNT)
--
Martin Michlmayr
http://www.cyrius.com/
