Message-Id: <1218566008.13866.41.camel@localhost>
Date:	Tue, 12 Aug 2008 20:33:28 +0200
From:	Milan Plzik <milan.plzik@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Timer unstability on when using C2 and deeper sleep states (Dell
	Latitude XT)

Good day,

  This e-mail will be a bit longer, as I will describe everything I was
able to find out about $subj. I'm not 100% sure that the issue is what
it seems to be (not even sure I'm posting to correct mailing list), so
if you see I did something wrong, please tell me. Also please, Cc: me,
as I'm not (yet, I was not able to find out how) subscribed to this
mailing list.

  I started to experiment with Linux on Dell Latitude XT, actually with
2.6.26 (for more info see [1]). The system seems to be more or less
operational, when booting without any special arguments, but sometimes
it hangs for few seconds with no reason. This becomes more apparent when
e.g. playing movie (player sometimes stops for really long while), and
is also apparent when using powertop, which tells me I had 20000
wakeups/s (yes, twenty thousand) per second, although sum of wakeups
from the topmost wakeup causes does not reach 2000. Sometimes, however,
this number goes down to reasonable values, but only for a while.

  I spent some time experimenting with linux kernel parameters; first
with clocksource, where with all possible sources (but jiffies, which
seemed to work) were having the same problem. With nohz=off parameter
the computer was stable (but it did not enter power saving states), and
after trying processor.max_cstate=1, computer was stable as well (any
higher state causes instability) and powertop was returning meaningful
values.

  Any attempts I made failed, so I'll welcome any suggestion, I have
never seen something like this before.

  Best regards,
	Milan Plzik


[1] My configuration follows:

# uname -a
Linux tiny 2.6.26-gentoo #18 SMP Tue Aug 12 12:40:57 CEST 2008 x86_64 Intel(R) Core(TM)2 CPU U7600 @ 1.20GHz GenuineIntel GNU/Linux

# grep -e HZ -e HPET -e RTC -e IDLE -e CPUFREQ /usr/src/linux/.config |grep -v "not set"
CONFIG_ARCH_HAS_CPU_IDLE_WAIT=y
CONFIG_NO_HZ=y
CONFIG_HPET_TIMER=y
CONFIG_HPET_EMULATE_RTC=y
CONFIG_HZ_1000=y
CONFIG_HZ=1000
CONFIG_X86_ACPI_CPUFREQ=y
CONFIG_X86_ACPI_CPUFREQ_PROC_INTF=y
CONFIG_CPU_IDLE=y
CONFIG_CPU_IDLE_GOV_LADDER=y
CONFIG_CPU_IDLE_GOV_MENU=y
CONFIG_HPET=y
CONFIG_HPET_MMAP=y
CONFIG_RTC_LIB=y
CONFIG_RTC_CLASS=y
CONFIG_RTC_HCTOSYS=y
CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
# RTC interfaces
CONFIG_RTC_INTF_SYSFS=y
CONFIG_RTC_INTF_PROC=y
CONFIG_RTC_INTF_DEV=y
CONFIG_RTC_INTF_DEV_UIE_EMUL=y
# I2C RTC drivers
# SPI RTC drivers
# Platform RTC drivers
CONFIG_RTC_DRV_CMOS=y
# on-CPU RTC drivers

# cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 15
model name	: Intel(R) Core(TM)2 CPU         U7600  @ 1.20GHz
stepping	: 2
cpu MHz		: 800.000
cache size	: 2048 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 2
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm
constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est
tm2 ssse3 cx16 xtpr lahf_lm
bogomips	: 2402.19
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 15
model name	: Intel(R) Core(TM)2 CPU         U7600  @ 1.20GHz
stepping	: 2
cpu MHz		: 800.000
cache size	: 2048 KB
physical id	: 0
siblings	: 2
core id		: 1
cpu cores	: 2
apicid		: 1
initial apicid	: 1
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm
constant_tsc arch_perfmon pebs bts rep_good pni monitor ds_cpl vmx est
tm2 ssse3 cx16 xtpr lahf_lm
bogomips	: 2400.00
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

# lspci
00:00.0 Host bridge: ATI Technologies Inc Device 7930
00:01.0 PCI bridge: ATI Technologies Inc Device 7932
00:04.0 PCI bridge: ATI Technologies Inc Device 7934
00:06.0 PCI bridge: ATI Technologies Inc Device 7936
00:07.0 PCI bridge: ATI Technologies Inc Device 7937
00:13.0 USB Controller: ATI Technologies Inc SB600 USB (OHCI0)
00:13.1 USB Controller: ATI Technologies Inc SB600 USB (OHCI1)
00:13.2 USB Controller: ATI Technologies Inc SB600 USB (OHCI2)
00:13.3 USB Controller: ATI Technologies Inc SB600 USB (OHCI3)
00:13.4 USB Controller: ATI Technologies Inc SB600 USB (OHCI4)
00:13.5 USB Controller: ATI Technologies Inc SB600 USB Controller (EHCI)
00:14.0 SMBus: ATI Technologies Inc SB600 SMBus (rev 14)
00:14.1 IDE interface: ATI Technologies Inc SB600 IDE
00:14.2 Audio device: ATI Technologies Inc SB600 Azalia
00:14.3 ISA bridge: ATI Technologies Inc SB600 PCI to LPC Bridge
00:14.4 PCI bridge: ATI Technologies Inc SB600 PCI to PCI Bridge
01:05.0 VGA compatible controller: ATI Technologies Inc Device 7942
03:01.0 CardBus bridge: Texas Instruments PCIxx12 Cardbus Controller
03:01.1 FireWire (IEEE 1394): Texas Instruments PCIxx12 OHCI Compliant
IEEE 1394 Host Controller
03:01.3 SD Host controller: Texas Instruments PCIxx12 SDA Standard
Compliant SD Host Controller
09:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5756ME
Gigabit Ethernet PCI Express
0b:00.0 Network controller: Broadcom Corporation BCM4310 USB Controller
(rev 01)


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