Re: ACPI PM-Timer rev.2 [Was: Re: ACPI PM-Timer [Was: Re: [RFC][PATCH] must fix lists]]

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To: Dominik Brodowski <linux@brodo.de>
Date:	04 Nov 2003 14:03:20 -0800

On Mon, 2003-10-27 at 15:01, Dominik Brodowski wrote:
> On Mon, Oct 27, 2003 at 11:07:19AM -0800, john stultz wrote:
> > Ah, OK. Well, I'd prefer the manual ACPI parsing personally, but having
> > tried and failed to implement it once myself, I'd more prefer not to do
> > it myself. ;)
>
> Here it is, and it is soooo much nicer than my previous implementation. It
> lacks the "lost-ticks compensation" and math cleanup John is working on, but
> otherwise:

Finally, here are my fixes to Dominik's patch (meant to send these out
last week, but got swamped). Basically it cleans up some of the math,
adds lost-tick compensation and monotonic_clock, fixes up a bit of the
ACPI table mapping, and moves the config option under the ACPI menu. Oh
yea, and it compiles, too ;)

Works well for me, but needs more testing.

Applies on top of Dominik's ACPI PM-timer rev.2 patch.
http://www.ussg.iu.edu/hypermail/linux/kernel/0310.3/0669.html

Many thanks to Dominik for the great work and getting this started.
-john

diff -Nru a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
--- a/Documentation/kernel-parameters.txt Tue Nov 4 13:30:42 2003
+++ b/Documentation/kernel-parameters.txt Tue Nov 4 13:30:42 2003
@@ -214,7 +214,7 @@
                         Forces specified timesource (if avaliable) to be used
                         when calculating gettimeofday(). If specicified timesource
                         is not avalible, it defaults to PIT.
- Format: { pit | tsc | cyclone | ... }
+ Format: { pit | tsc | cyclone | pmtmr }
 
         hpet= [IA-32,HPET] option to disable HPET and use PIT.
                         Format: disable
diff -Nru a/arch/i386/Kconfig b/arch/i386/Kconfig
--- a/arch/i386/Kconfig Tue Nov 4 13:30:42 2003
+++ b/arch/i386/Kconfig Tue Nov 4 13:30:42 2003
@@ -411,24 +411,6 @@
 config HPET_EMULATE_RTC
         def_bool HPET_TIMER && RTC=y
 
-config X86_PM_TIMER
- bool "Power Management Timer Support"
- depends on (!X86_VISWS && !X86_VISWS) && EXPERIMENTAL
- default n
- help
- The Power Management Timer is available on all ACPI-capable,
- in most cases even if ACPI is unusable or blacklisted.
-
- This timing source is not affected by powermanagement features
- like aggressive processor idling, throttling, frequency and/or
- voltage scaling, unlike the commonly used Time Stamp Counter
- (TSC) timing source.
-
- So, if you see messages like 'Losing too many ticks!' in the
- kernel logs, and/or you are using a this on a notebook which
- does not yet have an HPET (see above), you should say "Y"
- here. Otherwise, say "N".
-
 config SMP
         bool "Symmetric multi-processing support"
         ---help---
diff -Nru a/arch/i386/kernel/acpi/boot.c b/arch/i386/kernel/acpi/boot.c
--- a/arch/i386/kernel/acpi/boot.c Tue Nov 4 13:30:42 2003
+++ b/arch/i386/kernel/acpi/boot.c Tue Nov 4 13:30:42 2003
@@ -319,15 +319,19 @@
 }
 #endif
 
-/* detect the location of the ACPI PM Timer
+/* detect the location of the ACPI PM Timer */
 #ifdef CONFIG_X86_PM_TIMER
 extern u32 pmtmr_ioport;
 
 static int __init acpi_parse_fadt(unsigned long phys, unsigned long
size)
 {
- struct fadt_descriptor_rev2 *fadt;
+ struct fadt_descriptor_rev2 *fadt =0;
 
- fadt = __va(phys);
+ fadt = (struct fadt_descriptor_rev2*) __acpi_map_table(phys,size);
+ if(!fadt) {
+ printk(KERN_WARNING PREFIX "Unable to map FADT\n");
+ return 0;
+ }
 
         if (fadt->revision >= FADT2_REVISION_ID) {
                 /* FADT rev. 2 */
diff -Nru a/arch/i386/kernel/timers/timer_pm.c
b/arch/i386/kernel/timers/timer_pm.c
--- a/arch/i386/kernel/timers/timer_pm.c Tue Nov 4 13:30:42 2003
+++ b/arch/i386/kernel/timers/timer_pm.c Tue Nov 4 13:30:42 2003
@@ -30,7 +30,12 @@
 
 /* value of the Power timer at last timer interrupt */
 static u32 offset_tick;
+static u32 offset_delay;
 
+static unsigned long long monotonic_base;
+static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;
+
+#define ACPI_PM_MASK 0xFFFFFF /* limit it to 24 bits */
 
 static int init_pmtmr(char* override)
 {
@@ -62,23 +67,88 @@
         return -ENODEV;
 }
 
+static inline u32 cyc2us(u32 cycles)
+{
+ /* The Power Management Timer ticks at 3.579545 ticks per microsecond.
+ * 1 / PM_TIMER_FREQUENCY == 0.27936511 =~ 286/1024 [error: 0.024%]
+ *
+ * Even with HZ = 100, delta is at maximum 35796 ticks, so it can
+ * easily be multiplied with 286 (=0x11E) without having to fear
+ * u32 overflows.
+ */
+ cycles *= 286;
+ return (cycles >> 10);
+}
 
 /*
  * this gets called during each timer interrupt
  */
 static void mark_offset_pmtmr(void)
 {
+ u32 lost, delta, last_offset;
+ static int first_run = 1;
+ last_offset = offset_tick;
+
+ write_seqlock(&monotonic_lock);
+
         offset_tick = inl(pmtmr_ioport);
- offset_tick &= 0xFFFFFF; /* limit it to 24 bits */
+ offset_tick &= ACPI_PM_MASK; /* limit it to 24 bits */
+
+ /* calculate tick interval */
+ delta = (offset_tick - last_offset) & ACPI_PM_MASK;
+
+ /* convert to usecs */
+ delta = offset_delay + cyc2us(delta);
+
+ /* convert to ticks */
+ lost = delta/(USEC_PER_SEC/HZ);
+ offset_delay = delta%(USEC_PER_SEC/HZ);
+
+ /* update the monotonic base value */
+ monotonic_base += delta;
+ write_sequnlock(&monotonic_lock);
+
+
+ /* compensate for lost ticks */
+ if (lost >= 2)
+ jiffies += lost - 1;
+
+ /* don't calculate delay for first run,
+ or if we've got less then a tick */
+ if (first_run || (lost < 1)) {
+ first_run = 0;
+ offset_delay = 0;
+ }
+
         return;
 }
 
 
 static unsigned long long monotonic_clock_pmtmr(void)
 {
- return 0;
-}
+ u32 last_offset, this_offset;
+ unsigned long long base, ret;
+ unsigned seq;
+
 
+ /* atomically read monotonic base & last_offset */
+ do {
+ seq = read_seqbegin(&monotonic_lock);
+ last_offset = offset_tick;
+ base = monotonic_base;
+ } while (read_seqretry(&monotonic_lock, seq));
+
+
+ /* Read the cyclone counter */
+
+ this_offset = inl(pmtmr_ioport) & ACPI_PM_MASK;
+
+
+ /* convert to nanoseconds */
+ ret = base + ((this_offset - last_offset) & ACPI_PM_MASK);
+ ret = cyc2us(ret)*1000;
+ return ret;
+}
 
 /*
  * copied from delay_pit
@@ -106,21 +176,10 @@
 
         offset = offset_tick;
         now = inl(pmtmr_ioport);
- now &= 0xFFFFFF;
- if (likely(offset < now))
- delta = now - offset;
- else if (offset > now)
- delta = (0xFFFFFF - offset) + now;
+ now &= ACPI_PM_MASK;
+ delta = (now - offset)&ACPI_PM_MASK;
 
- /* The Power Management Timer ticks at 3.579545 ticks per microsecond.
- * 1 / PM_TIMER_FREQUENCY == 0.27936511 =~ 286/1024 [error: 0.024%]
- *
- * Even with HZ = 100, delta is at maximum 35796 ticks, so it can
- * easily be multiplied with 286 (=0x11E) without having to fear
- * u32 overflows.
- */
- delta *= 286;
- return (unsigned long) (delta >> 10);
+ return (unsigned long) offset_delay + cyc2us(delta);
 }
 
 
diff -Nru a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
--- a/drivers/acpi/Kconfig Tue Nov 4 13:30:42 2003
+++ b/drivers/acpi/Kconfig Tue Nov 4 13:30:42 2003
@@ -269,5 +269,24 @@
           particular, many Toshiba laptops require this for correct operation
           of the AC module.
 
+config X86_PM_TIMER
+ bool "Power Management Timer Support"
+ depends on X86 && ACPI
+ depends on ACPI_BOOT && EXPERIMENTAL
+ default n
+ help
+ The Power Management Timer is available on all ACPI-capable,
+ in most cases even if ACPI is unusable or blacklisted.
+
+ This timing source is not affected by powermanagement features
+ like aggressive processor idling, throttling, frequency and/or
+ voltage scaling, unlike the commonly used Time Stamp Counter
+ (TSC) timing source.
+
+ So, if you see messages like 'Losing too many ticks!' in the
+ kernel logs, and/or you are using a this on a notebook which
+ does not yet have an HPET (see above), you should say "Y"
+ here.
+
 endmenu
 

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• Previous message: Ulrich Drepper: "Re: ext3 performance inconsistencies, 2.4/2.6"
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