Re: gettimeofday order of magnitude slower with pmtimer, which is default

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

john stultz <johnstul@us.ibm.com> writes:

> In my TOD rework I've dropped the triple read, figuring if a problem
> arose we could blacklist the specific box. This patch covers that, so it
> looks like a good idea to me.
>
> I've not tested it myself, but if you feel good about it, please send it
> to Andrew.

Current patch is the following. If I'm missing something, or you have
some comment, please tell me. (Since I don't have ICH4, ICH4 detection
is untested)

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>



Current timer_pm.c reads I/O port triple times, in order to avoid the
bug of chipset. But I/O port is slow.

2.6.16 (pmtmr)
Simple gettimeofday: 3.6532 microseconds

2.6.16+patch (pmtmr)
Simple gettimeofday: 1.4582 microseconds

[if chip is buggy, probably it will be 7us or more in 4.2% of probability.]


This patch adds blacklist of buggy chip, and if chip is not buggy,
this uses fast normal version instead of slow workaround version.

If chip is buggy, warnings "pmtmr is slow". But sounds like there is
gray zone. I found the PIIX4 errata, but I couldn't find the ICH4
errata.  But some motherboard seems to have problem.

So, if found a ICH4, also warnings, and uses a workaround version.  If
user's ICH4 is good actually, user can specify the "pmtmr_good" boot
parameter to use fast version.


Acked-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---

 arch/i386/kernel/timers/timer_pm.c |   99 +++++++++++++++++++++++++++++++------
 1 file changed, 84 insertions(+), 15 deletions(-)

diff -puN arch/i386/kernel/timers/timer_pm.c~pm-kill-workaround arch/i386/kernel/timers/timer_pm.c
--- linux-2.6/arch/i386/kernel/timers/timer_pm.c~pm-kill-workaround	2006-03-22 06:09:15.000000000 +0900
+++ linux-2.6-hirofumi/arch/i386/kernel/timers/timer_pm.c	2006-03-22 06:09:23.000000000 +0900
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/init.h>
+#include <linux/pci.h>
 #include <asm/types.h>
 #include <asm/timer.h>
 #include <asm/smp.h>
@@ -35,7 +36,6 @@
  * in arch/i386/acpi/boot.c */
 u32 pmtmr_ioport = 0;
 
-
 /* value of the Power timer at last timer interrupt */
 static u32 offset_tick;
 static u32 offset_delay;
@@ -45,24 +45,93 @@ static seqlock_t monotonic_lock = SEQLOC
 
 #define ACPI_PM_MASK 0xFFFFFF /* limit it to 24 bits */
 
+static int pmtmr_need_workaround __read_mostly = 1;
+
+static int __init pmtr_good_setup(char *__str)
+{
+	pmtmr_need_workaround = 0;
+	return 0;
+}
+__setup("pmtmr_good", pmtr_good_setup);
+
+#ifdef CONFIG_PCI
+/*
+ * PIIX4 Errata:
+ *
+ * The power management timer may return improper result when read.
+ * Although the timer value settles properly after incrementing,
+ * while incrementing there is a 3 ns window every 69.8 ns where the
+ * timer value is indeterminate (a 4.2% chance that the data will be
+ * incorrect when read). As a result, the ACPI free running count up
+ * timer specification is violated due to erroneous reads.
+ */
+static int __init pmtmr_bug_check(void)
+{
+	const struct pci_device_id gray_list[] = {
+		/* these chipsets may have bug. */
+		{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82801DB_0) },
+		{ },
+	};
+	struct pci_dev *dev;
+	int pmtmr_has_bug = 0;
+	u8 rev;
+
+	if (!pmtmr_need_workaround)
+		return 0;
+
+	dev = pci_get_device(PCI_VENDOR_ID_INTEL,
+			     PCI_DEVICE_ID_INTEL_82371AB_3, NULL);
+	if (dev) {
+		pci_read_config_byte(dev, PCI_REVISION_ID, &rev);
+		/* the bug has been fixed in PIIX4M */
+		if (rev < 3) {
+			printk(KERN_WARNING
+			       "* Found PM-Timer Bug on this chip. For workarounds a bug, this timer\n"
+			       "* source is slow. Other timer source may be proper (clock=)\n");
+			pmtmr_has_bug = 1;
+		}
+		pci_dev_put(dev);
+	}
+
+	if (pci_dev_present(gray_list)) {
+		printk(KERN_WARNING
+		       "* This chipset may have PM-Timer Bug, For workarounds a bug,\n"
+		       "* this timer source is slow. If you are sure, please use \"pmtmr_good\"\n"
+		       "* for disabling the workaround\n");
+		pmtmr_has_bug = 1;
+	}
+
+	if (!pmtmr_has_bug)
+		pmtmr_need_workaround = 0;
+
+	return 0;
+}
+device_initcall(pmtmr_bug_check);
+#endif
+
 /*helper function to safely read acpi pm timesource*/
 static inline u32 read_pmtmr(void)
 {
-	u32 v1=0,v2=0,v3=0;
-	/* It has been reported that because of various broken
-	 * chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time
-	 * source is not latched, so you must read it multiple
-	 * times to insure a safe value is read.
-	 */
-	do {
-		v1 = inl(pmtmr_ioport);
-		v2 = inl(pmtmr_ioport);
-		v3 = inl(pmtmr_ioport);
-	} while ((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1)
-			|| (v3 > v1 && v3 < v2));
+	if (pmtmr_need_workaround) {
+		u32 v1, v2, v3;
+
+		/* It has been reported that because of various broken
+		 * chipsets (ICH4, PIIX4 and PIIX4E) where the ACPI PM time
+		 * source is not latched, so you must read it multiple
+		 * times to insure a safe value is read.
+		 */
+		do {
+			v1 = inl(pmtmr_ioport);
+			v2 = inl(pmtmr_ioport);
+			v3 = inl(pmtmr_ioport);
+		} while ((v1 > v2 && v1 < v3) || (v2 > v3 && v2 < v1)
+			 || (v3 > v1 && v3 < v2));
+
+		/* mask the output to 24 bits */
+		return v2 & ACPI_PM_MASK;
+	}
 
-	/* mask the output to 24 bits */
-	return v2 & ACPI_PM_MASK;
+	return inl(pmtmr_ioport) & ACPI_PM_MASK;
 }
 
 
_
-
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