From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Grundler Subject: Re: [parisc-linux] [PATCH] timer_interrupt and gettimeoffset. Date: Fri, 1 Sep 2006 16:48:25 -0600 Message-ID: <20060901224825.GD4041@colo.lackof.org> References: <119aab440608292148s4ee3ffb0xaac62a74c0f1403b@mail.gmail.com> <20060831065327.GG3999@colo.lackof.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: parisc-linux To: Carlos O'Donell Return-Path: In-Reply-To: <20060831065327.GG3999@colo.lackof.org> List-Id: parisc-linux developers list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: parisc-linux-bounces@lists.parisc-linux.org On Thu, Aug 31, 2006 at 12:53:27AM -0600, Grant Grundler wrote: > And I've hacked your version some more. > diff is below. version #3: seems to be working fine on 64-bit SMP. 32-bit UP kernel is still under construction. That means gettimeoffset() hasn't been tested. And I'm getting the following warnings on my b2600: ... Setting the system clock.. timer_interrupt(CPU 0): delayed! run ntpdate ticks 859 cycles FFF51A1C rem 40E59C next/now FFFE7A9D/96080 gettimeoffset(CPU -119762782): missing ticks!cycles FFC87AE4 prev/now/next 6EBEA41/14C624/4C4B40 clock 0 gettimeoffset(CPU -177625053): missing ticks!cycles FFC87AE4 prev/now/next A5ED2C0/14C624/4C4B40 clock 12 gettimeoffset(CPU -238800592): missing ticks!cycles FFC87AE4 prev/now/next E0449B3/14C624/4C4B40 clock 12 gettimeoffset(CPU -302979574): missing ticks!cycles FFC87AE4 prev/now/next 11D794D9/14C624/4C4B40 clock 0 Sysgettimeoffset(CPU -361861366): missing ticks!cycles FFC87AE4 prev/now/next 155A0BD9/14C624/4C4B40 clock 12 tem Clock set. Local time: Fri Sep 1 22:42:09 UTC 2006. gettimeoffset printk is busticated. I'll fix that in the next version. But it looks like wrapped values are causing problems. The timer_interrupt warning might be reasonable given we are making a call to firmware to set the clock and block interrupts for the duration. In addition to time.c, two more files are touched: smp.c I couldn't see where slave CPUs would start the interval timer and added the call here. param.h Use CONFIG_HZ for interval timer. We were ignored this before. I just realized one small change to arch/parisc/kernel/processor.c is missin from this diff. We don't want processor_probe() to clobber CPU0's cpu_data. "it_value" has already been initialized. enjoy! grant diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c index 98e4095..f33e8de 100644 --- a/arch/parisc/kernel/smp.c +++ b/arch/parisc/kernel/smp.c @@ -430,8 +430,9 @@ smp_do_timer(struct pt_regs *regs) static void __init smp_cpu_init(int cpunum) { - extern int init_per_cpu(int); /* arch/parisc/kernel/setup.c */ + extern int init_per_cpu(int); /* arch/parisc/kernel/processor.c */ extern void init_IRQ(void); /* arch/parisc/kernel/irq.c */ + extern void start_cpu_itimer(void); /* arch/parisc/kernel/time.c */ /* Set modes and Enable floating point coprocessor */ (void) init_per_cpu(cpunum); @@ -457,6 +458,7 @@ smp_cpu_init(int cpunum) enter_lazy_tlb(&init_mm, current); init_IRQ(); /* make sure no IRQ's are enabled or pending */ + start_cpu_itimer(); } diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c index 5facc9b..337c4ec 100644 --- a/arch/parisc/kernel/time.c +++ b/arch/parisc/kernel/time.c @@ -35,8 +35,8 @@ #include /* xtime and wall_jiffies keep wall-clock time */ extern unsigned long wall_jiffies; -static long clocktick __read_mostly; /* timer cycles per tick */ -static long halftick __read_mostly; +static unsigned long clocktick __read_mostly; /* timer cycles per tick */ +static unsigned long halftick __read_mostly; #ifdef CONFIG_SMP extern void smp_do_timer(struct pt_regs *regs); @@ -44,34 +44,77 @@ #endif irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) { - long now; - long next_tick; - int nticks; + unsigned long now; + unsigned long next_tick; + unsigned long cycles_elapsed; + unsigned long cycles_remainder; + unsigned long ticks_elapsed = 1; /* at least one elapsed */ int cpu = smp_processor_id(); profile_tick(CPU_PROFILING, regs); - now = mfctl(16); - /* initialize next_tick to time at last clocktick */ + /* Initialize next_tick to the expected tick time. */ next_tick = cpu_data[cpu].it_value; - /* since time passes between the interrupt and the mfctl() - * above, it is never true that last_tick + clocktick == now. If we - * never miss a clocktick, we could set next_tick = last_tick + clocktick - * but maybe we'll miss ticks, hence the loop. - * - * Variables are *signed*. + /* Get current interval timer. + * CR16 reads as 64 bits in CPU wide mode. + * CR16 reads as 32 bits in CPU narrow mode. */ + now = mfctl(16); + + cycles_elapsed = now - next_tick; + + /* Determine how much time elapsed. */ + if (now < next_tick) { + /* Scenario 2: CR16 wrapped after clock tick. + * 1's complement will give us the "elapse cycles". + * + * This "cr16 wrapped" cruft is primarily for 32-bit kernels. + * So think "unsigned long is u32" when reading the code. + * And yes, of course 64-bit will someday wrap, but only + * every 198841 days on a 1GHz machine. + */ + cycles_elapsed = ~cycles_elapsed; /* off by one cycle - don't care */ + } + + ticks_elapsed += cycles_elapsed / clocktick; + cycles_remainder = cycles_elapsed % clocktick; - nticks = 0; - while((next_tick - now) < halftick) { - next_tick += clocktick; - nticks++; + /* Can we differentiate between "early CR16" (aka Scenario 1) and + * "long delay" (aka Scenario 3)? I don't think so. + * + * We expected timer_interrupt to be delivered at least a few hundred + * cycles after the IT fires. But it's arbitrary how much time passes + * before we call it "late". I've picked one second. + */ + if (ticks_elapsed > HZ) { + /* Scenario 3: very long delay? bad in any case */ + printk (KERN_CRIT "timer_interrupt(CPU %d): delayed! run ntpdate" + " ticks %ld cycles %lX rem %lX" + " next/now %lX/%lX\n", + cpu, + ticks_elapsed, cycles_elapsed, cycles_remainder, + next_tick, now ); + + ticks_elapsed = 1; /* hack to limit damage in loop below */ } + + + /* Determine when (in CR16 cycles) next IT interrupt will fire. + * We want IT to fire modulo clocktick even if we miss/skip some. + * But those interrupts don't in fact get delivered that regularly. + */ + next_tick = now + (clocktick - cycles_remainder); + + /* Program the IT when to deliver the next interrupt. */ + /* Only bottom 32-bits of next_tick are written to cr16. */ mtctl(next_tick, 16); cpu_data[cpu].it_value = next_tick; - while (nticks--) { + /* Now that we are done mucking with unreliable delivery of interrupts, + * go do system house keeping. + */ + while (ticks_elapsed--) { #ifdef CONFIG_SMP smp_do_timer(regs); #else @@ -124,21 +167,40 @@ #ifndef CONFIG_SMP * Once parisc-linux learns the cr16 difference between processors, * this could be made to work. */ - long last_tick; - long elapsed_cycles; + unsigned long now; + unsigned long prev_tick; + unsigned long next_tick; + unsigned long elapsed_cycles; + unsigned long usec; - /* it_value is the intended time of the next tick */ - last_tick = cpu_data[smp_processor_id()].it_value; + next_tick = cpu_data[smp_processor_id()].it_value; + now = mfctl(16); /* Read the hardware interval timer. */ - /* Subtract one tick and account for possible difference between - * when we expected the tick and when it actually arrived. - * (aka wall vs real) - */ - last_tick -= clocktick * (jiffies - wall_jiffies + 1); - elapsed_cycles = mfctl(16) - last_tick; + prev_tick = next_tick - clocktick; - /* the precision of this math could be improved */ - return elapsed_cycles / (PAGE0->mem_10msec / 10000); + /* Assume Scenario 1: "now" is later than prev_tick. */ + elapsed_cycles = now - prev_tick; + + if (now < prev_tick) { + /* Scenario 2: CR16 wrapped! + * 1's complement is close enough. + */ + elapsed_cycles = ~elapsed_cycles; + } + + if (elapsed_cycles > (HZ * clocktick)) { + /* Scenario 3: clock ticks are missing. */ + printk (KERN_CRIT "gettimeoffset(CPU %d): missing ticks!" + "cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n", + elapsed_cycles, prev_tick, now, next_tick, clocktick); + } + + /* FIXME: Can we improve the precision? Not with PAGE0. */ + usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec; + + /* add in "lost" jiffies */ + usec += clocktick * (jiffies - wall_jiffies); + return usec; #else return 0; #endif @@ -149,6 +211,7 @@ do_gettimeofday (struct timeval *tv) { unsigned long flags, seq, usec, sec; + /* Hold xtime_lock and adjust timeval. */ do { seq = read_seqbegin_irqsave(&xtime_lock, flags); usec = gettimeoffset(); @@ -156,25 +219,13 @@ do_gettimeofday (struct timeval *tv) usec += (xtime.tv_nsec / 1000); } while (read_seqretry_irqrestore(&xtime_lock, seq, flags)); - if (unlikely(usec > LONG_MAX)) { - /* This can happen if the gettimeoffset adjustment is - * negative and xtime.tv_nsec is smaller than the - * adjustment */ - printk(KERN_ERR "do_gettimeofday() spurious xtime.tv_nsec of %ld\n", usec); - usec += USEC_PER_SEC; - --sec; - /* This should never happen, it means the negative - * time adjustment was more than a second, so there's - * something seriously wrong */ - BUG_ON(usec > LONG_MAX); - } - - + /* Move adjusted usec's into sec's. */ while (usec >= USEC_PER_SEC) { usec -= USEC_PER_SEC; ++sec; } + /* Return adjusted result. */ tv->tv_sec = sec; tv->tv_usec = usec; } @@ -226,22 +277,24 @@ unsigned long long sched_clock(void) } +void __init start_cpu_itimer(void) +{ + unsigned int cpu = smp_processor_id(); + unsigned long next_tick = mfctl(16) + clocktick; + + mtctl(next_tick, 16); /* kick off Interval Timer (CR16) */ + + cpu_data[cpu].it_value = next_tick; +} + void __init time_init(void) { - unsigned long next_tick; static struct pdc_tod tod_data; clocktick = (100 * PAGE0->mem_10msec) / HZ; halftick = clocktick / 2; - /* Setup clock interrupt timing */ - - next_tick = mfctl(16); - next_tick += clocktick; - cpu_data[smp_processor_id()].it_value = next_tick; - - /* kick off Itimer (CR16) */ - mtctl(next_tick, 16); + start_cpu_itimer(); /* get CPU 0 started */ if(pdc_tod_read(&tod_data) == 0) { write_seqlock_irq(&xtime_lock); diff --git a/include/asm-parisc/param.h b/include/asm-parisc/param.h index 07cb9b9..32e03d8 100644 --- a/include/asm-parisc/param.h +++ b/include/asm-parisc/param.h @@ -2,13 +2,9 @@ #ifndef _ASMPARISC_PARAM_H #define _ASMPARISC_PARAM_H #ifdef __KERNEL__ -# ifdef CONFIG_PA20 -# define HZ 1000 /* Faster machines */ -# else -# define HZ 100 /* Internal kernel timer frequency */ -# endif -# define USER_HZ 100 /* .. some user interfaces are in "ticks" */ -# define CLOCKS_PER_SEC (USER_HZ) /* like times() */ +#define HZ CONFIG_HZ +#define USER_HZ 100 /* some user API use "ticks" */ +#define CLOCKS_PER_SEC (USER_HZ) /* like times() */ #endif #ifndef HZ _______________________________________________ parisc-linux mailing list parisc-linux@lists.parisc-linux.org http://lists.parisc-linux.org/mailman/listinfo/parisc-linux