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kernel debugging nodes missing from /sys/kernel
by amit mehta June 27, 2011

June 27, 2011

I've two 64 bit machines,both have Linux kernel running, but on one of the machines I'm not seeing any node under /sys/kernel/debug. I checked some config(CONFIG_*) in the kernel configuration file on both machines but they seem to be the same. More information below: 1: SuseX86_64:~ # uname -a Linux SuseX86_64 2.6.32.12-0.7-default #1 SMP 2010-05-20 11:14:20 +0200 x86_64 x86_64 x86_64 GNU/Linux SuseX86_64:~ # ls /sys/kernel/debug/ bdi dri dynamic_debug gpio ipoib kprobes mce sched_features slow_work usb x86 SuseX86_64:~ # grep ^CONFIG_DEBUG /boot/config-2.6.32.12-0.7-default CONFIG_DEBUG_FS=y CONFIG_DEBUG_KERNEL=y CONFIG_DEBUG_BUGVERBOSE=y CONFIG_DEBUG_INFO=y CONFIG_DEBUG_MEMORY_INIT=y CONFIG_DEBUG_BLOCK_EXT_DEVT=y CONFIG_DEBUG_FORCE_WEAK_PER_CPU=y CONFIG_DEBUG_RODATA=y SuseX86_64:~ # cat /etc/SuSE-release SUSE Linux Enterprise Server 11 (x86_64) VERSION = 11 PATCHLEVEL = 1 2: Now on a different machine, here I don't see the kernel/debug nodes under /sys FS [root@redhatx86_64]# uname -a Linux lredhatx86_64 2.6.32-71.el6.x86_64 #1 SMP Wed Sep 1 01:33:01 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux [root@redhatx86_64 ~]# cat /etc/redhat-release Red Hat Enterprise Linux Server release 6.0 (Santiago) [root@redhatx86_64 ~]# ls -l /sys/kernel/debug/ total 0 < -- ------------ ----------- [root@redhatx86_64 ]# grep ^CONFIG_DEBUG /boot/config-2.6.32-71.el6.x86_64 CONFIG_DEBUG_FS=y CONFIG_DEBUG_KERNEL=y CONFIG_DEBUG_SHIRQ=y CONFIG_DEBUG_NMI_TIMEOUT=30 CONFIG_DEBUG_BUGVERBOSE=y CONFIG_DEBUG_INFO=y CONFIG_DEBUG_MEMORY_INIT=y CONFIG_DEBUG_LIST=y CONFIG_DEBUG_FORCE_WEAK_PER_CPU=y CONFIG_DEBUG_STACKOVERFLOW=y CONFIG_DEBUG_RODATA=y CONFIG_DEBUG_RODATA_TEST=y CONFIG_DEBUG_NX_TEST=m CONFIG_DEBUG_BOOT_PARAMS=y I'm specifically interested in /sys/kernel/debug/kprobes/enabled According to kprobes.txt(http://lxr.linux.no/linux+v2.6.39/Documentation/kprobes.txt#L692) I can enable/disable kprobes infrastructure through this node. Though on both these two servers, I was successfully insert and test some modules using kprobes. Please let me know what I'm missing on server2( redhatx86_64 ) Regards, Amit -- Life is elsewhere. Cross Frontiers. Fly away. - Salman Rushdie

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questions about the codingstyle in linux kernel.
by B tw June 26, 2011

June 26, 2011

Why the coding style in include/linux/page-flags.h is Camel Case? It is so ugly and uncoordinated.

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Re: Verify the frequency of a core
by pradeep hettiarachchi June 24, 2011

June 24, 2011

Hi Tharindu, Re: great effort, unfortunately what you mentioned does not verify the required fact (In other words, (1) your method requests the governor to do the frequency change request (FCR), (2) the governor ask the driver to do the job (trace the kernel code path, you will understand this). But internally, the CPU has single VID set, which request the motherboard regulator to change the Vcc. Motherboard (DC-to-DC) regulator does not have any way of setting different voltages for individual cores simultaneously. So, different core frequencies are not possible. However, (still I did not study the code), the scheduler might take the assigned frequency (by the user) into account when it schedule any task in the core (might be load balancing: to be confirmed) still no multiple frequencies are possible ). The informed frequency from sysfile is not accurate (the low lever drivers are not even called when you ask governor (sysfiles) to read the frequency): if you change the CPU frequency by other means (eg using writing directly to MSR), your sysfiles does not catch it. Have a look at low level implementation of frequency driver (they all change the frequency of the processor using MSR- a set of registers that specifically used to manage the CPU functionality and the configuration) So, if you want to verify that the CPU cores can stay in multiple frequencies simultaneously, the best method is to change the frequency by user-space governor and try to verify the frequency using direct MSRs (I did that and found which is not possible). If you can successfully show that, let me know. Sincerely, Pradeep M. Hettiarachchi On Thu, Jun 23, 2011 at 9:52 PM, Tharindu Rukshan Bamunuarachchi <btharindu(a)gmail.com> wrote: > Hi Pradeep, > > Below commands will do the job. > > modprobe acpi-cpufreq > modprobe cpufreq_userspace > > cd /sys/devices/system/cpu/cpu0/cpufreq > echo userspace > scaling_governor > echo 2394000 > scaling_setspeed > > cd /sys/devices/system/cpu/cpu1/cpufreq > echo userspace > scaling_governor > echo 2128000 > scaling_setspeed > > cd /sys/devices/system/cpu/cpu2/cpufreq > echo userspace > scaling_governor > echo 1862000 > scaling_setspeed > > cd /sys/devices/system/cpu/cpu3/cpufreq > echo userspace > scaling_governor > echo 1596000 > scaling_setspeed > > cat /proc/cpuinfo | grep MHz > cpu MHz : 2394.000 > cpu MHz : 2128.000 > cpu MHz : 1862.000 > cpu MHz : 1596.000 > > Tested on Q6600 > quadcore:~ # cat /proc/cpuinfo | grep GHz > model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz > model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz > model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz > model name : Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz > > > __ > Tharindu "Rukshan" Bamunuarachchi > > > > > > > On Fri, Jun 24, 2011 at 3:17 AM, pradeep hettiarachchi <pacprnt(a)gmail.com> > wrote: >> >> Hi Tharindu, >> >> An another round of the old questions: >> >> Can you give me any evidence to confirm that the core frequencies can >> be run in different values from each other. You may try to do (set >> individual core frequency values) it individually through any governor >> or MSR methods. However, actually it does not implemented internally. >> Please show/tell me if you have any methods to show that core >> frequencies are different at any given time. (Take i7 950 or Q 6600 >> processors applicable approach so that I can verify it so easily) >> >> >> >> >> Sincerely, >> >> Pradeep M. Hettiarachchi >> >> >> >> On Sat, Dec 25, 2010 at 2:45 PM, pradeep hettiarachchi >> <pacprnt(a)gmail.com> wrote: >> > Hi, >> > >> > Here what I did: >> > I set the "performance" governor for one of the cores and "ondemand" >> > governor on an another core. Then I noticed that the cores have >> > different frequencies. >> > Based of the above observation on different processors, I have a >> > couple of questions. >> > >> > 1) When I tried to frequency-scale in a core i7 processor, it allows >> > me to set different governors for individual cores. As per to my >> > understanding, the processor has 4 physical cores and 2 hardware >> > threads per core. (totaling 8 cores altogether) This means, I should >> > not be able to set different frequencies in two adjacent cores (say >> > core 0 and core 1) as they both same hardware. My understanding is I >> > should not be able to set the individual core frequencies as explained >> > above. >> > >> > 2) When I played with Q6600 processor, I found that trough the >> > governor, I can set the individual core-frequency. But as per to the >> > literature, Intel does not provide a facility to frequency-scale in >> > individual cores but the frequency in the entire processor. >> > >> > 3) What does the governor do? Does it set the frequency of the core >> > directly ? >> > >> > 4) Is there any way that I can verify the actual frequency of a core >> > other than the interface of the governor. Do you recommend to use MSR >> > direly to change and measure the frequency of the system ? >> > >> > >> > >> > >> > Sincerely, >> > >> > Pradeep M. Hettiarachchi >> > > >

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ipmicmd for bios settings
by C K Kashyap June 24, 2011

June 24, 2011

Hi, Is there a way to get the BIOS settings using ipmicmd? I'd appreciate it very much if you could provide me with an example usage. What I am looking for is a way to read the BIOS settings of a remote server. Regards, Kashyap

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Is this a Bug?
by Christian Deussen June 23, 2011

June 23, 2011

Hi, I just compiled my first Kernel from linus' tree and saw a warning in "sound/soc/codecs/wm8958-dsp2.c". I think a found a bug, but I am not sure. And I don`t want to waste the Kernel-dev's time on the lkml. In function wm8958_dsp2_fw(), at line 64, there is an uninitialized variable used. u32 data 32; ... /*not related code*/ ... if (memcmp(fw->data, "WMFW", 4) != 0) { dev_err(codec->dev, "%s: firmware has bad file magic %08x\n", name, data32); //shouldn't fw->data be used? goto err; } Am I right? And does this detail matter anyway? I made several small fixes for warnings and added some #ifdef CONFIG_BLA when code wasnt used. Are those changes welcome on the LKML? Thanks for your time.

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Re: make error in building sample code!
by loody June 23, 2011

June 23, 2011

hi : sorry for pick up this old thread. 2009/8/4 Robert P. J. Day <rpjday(a)crashcourse.ca>: > On Tue, 4 Aug 2009, Greg Peter wrote: > >> Hello, >> >> I am trying to build LDD3 sample code, just to get expirement around. >> (Obtained from the link -> >> http://oreilly.com.cn/codeexample/ldd3/examples.tar.gz) >> >> But I get the following errors when I run make: (PS note, I have the kernel >> source and headers installed) >> >> >> #examples> make >> for n in misc-progs misc-modules skull scull scullc sculld scullp scullv >> sbull snull short shortprint pci simple usb tty lddbus; do make -C $n || >> exit 1; done >> make[1]: Entering directory `/home/gregp/examples/misc-progs' >> cc -O2 -fomit-frame-pointer -Wall >> -I/lib/modules/2.6.27.23-0.1-pae/build/include setlevel.c -o setlevel >> setlevel.c:30: error: expected declaration specifiers or ?...? before ?syslog? >> setlevel.c:30: error: expected declaration specifiers or ?...? before ?type? >> setlevel.c:30: error: expected declaration specifiers or ?...? before ?bufp? >> setlevel.c:30: error: expected declaration specifiers or ?...? before ?len? >> setlevel.c:30: warning: data definition has no type or storage class >> setlevel.c:30: warning: type defaults to ?int? in declaration of ?_syscall3? >> setlevel.c: In function ?main?: >> setlevel.c:41: warning: implicit declaration of function ?syslog? >> make[1]: *** [setlevel] Error 1 >> make[1]: Leaving directory `/home/gregp/examples/misc-progs' >> make: *** [subdirs] Error 1 > > those userspace programs still use the now-deprecated and > unsupported _syscall macros. they should be rewritten to use > syscall() instead. see: > > http://www.kernel.org/doc/man-pages/online/pages/man2/_syscall.2.html > I can compile the attach lddbus.c successfully but fail to insert the module. it is because device_register return a non-zero value. I have also checked other driver to compare the procedure of initial "struct device", but I cannot see the difference. take scsi_debug.c for example: static struct device pseudo_primary = { .init_name = "pseudo_0", .release = pseudo_0_release, }; static int __init scsi_debug_init(void) { ...... ret = device_register(&pseudo_primary); if (ret < 0) { printk(KERN_WARNING "scsi_debug: device_register error: %d\n", ret); goto free_vm; } ..... } is there any CONFIG in kernel i should open for fixing this problem? -- Regards,

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questions for Linus
by Mulyadi Santosa June 23, 2011

June 23, 2011

Hi Greg.. I came with these questions for Linus, hope you're kind enough to collect it and forward it to Linus in LinuxCon: 1. When will Linux 2.8.x start? and what are the plans regarding the development model? do we back in dual 2.4.x/2.5x era? personally I think that model is nice.... makes one really know which tree to follow when he needs stable one, or the devel one... 2. I saw task/process scheduler is one that under heavy concern lately, take a look on "200 line patch that does wonder" for example. I am thinking, we better really incorporate pluggable scheduler framework, that enable us to change scheduling core algorithm on the fly. What do you think? 3. I read somewhere that once Coverity helps Linux kernel developers found out unseen bugs using sophisticated static code analysis. Is that still happening now? Probably a good deal, squashing bugs in nowadays kernel's size is pretty hard, I could say.. that's all for now Greg...thanks in advance...hopefully it's still make it.. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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spin locks
by Venkateswarlu P June 23, 2011

June 23, 2011

can anyone help in the implementation of spin locks in kernel source i go through the relevant header files and found various debugging CONFIG options in the struct i want the code without debugging features and the function spin_lock() spin_unlock() implementation I understood major part but unable to find the correct source

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how to implement a SCSI commands through a driver?
by RKK June 22, 2011

June 22, 2011

Hi all , Im trying to implement a custom new storage protocl which uses SCSI for storage in Linux . I have been looking around for some files in the Linux SCSI subsystems to understand its three layered design. The idea is to develop a separate stack which will internally use SCSI . so to get started all i want to do is write a module(kernel space) which sends SCSI commands to target device and retrieve some information from it. any idea like to how to proceed and which are files/books that can help me in this regard. I'm reading SCSI SPC-4 and SBC-3 specifications .

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Re: threading problem
by Daniel Baluta June 22, 2011

June 22, 2011

Hello Murali, > I have a device driver which provides the IOCTL function for the > application to interact. > > when the application sends the IOCTL CMD_GO, my driver has to toggle a > GPIO every 500 m Sec. until a 3 minute timeout occurs or a CMD_STOP > IOCTL is received. > > I tried the DECLARE_WORK, DECLARE_DELAYED_WORK and also > kernel_thread() to meet this requirement with no success. > Could you please show us the code? thanks, Daniel.

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