May 2012 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Finding the interrupt vector of a given IRQ
by Mark Farnell Oct. 20, 2012

Oct. 20, 2012

In the kernel, how can I find out the interrupt vector number of a given IRQ (for example, IRQ7)? Within the kernel module, I would like to manually set the IRQ using the assembly code: asm("int $<irq vector>"); and let the IRQ handler installed by a different module catch that interrupt. Is this possible? Thanks! Mark

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Porting my BSP to higher Kernel Versions
by Ramya Desai Aug. 24, 2012

Aug. 24, 2012

Dear Experts, I have a working BSP which runs on Kernel 2.6.10. Now I wanted to upgrade my BSP to higher versions like, 2.6.24. Is there any documentation/steps available to do so? Regards, Ramya

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some questions about log level
by loody June 29, 2012

June 29, 2012

hi all: my questions are below: 1. Can I temporarily let kernel message show in stdout? I google some key word as "console_loglevel" and I found following methods: a. echo 8 > /proc/sys/kernel/printk b. write a simple program which calling "klogctl(8, NULL, level)" Then I purposely connect/disconnect USB, but my console keep quiet. But dmesg shows connect/disconnect messages. 2. what is differences between above a and b methods? Are they not to used to change console_loglevel? 3. is it possible the max level of "console_loglevel" doesn't mean it will show on stdout? -- Thanks for your help

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identity mapped paging
by Vaibhav Jain June 19, 2012

June 19, 2012

I am not clear about the use of identity mapped paging while paging is being enabled by the operating system. Also I don't understand at what point are the identity mappings no longer useful.According to this article http://geezer.osdevbrasil.net/osd/mem/index.htm#identity - "The page table entries used to identity-map kernel memory can be deleted once paging and virtual addresses are enabled." Can somebody please explain? Thanks Vaibhav Jain

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Module vs Kernel main performacne
by Abu Rasheda June 9, 2012

June 9, 2012

Hi, I am working on x8_64 arch. Profiled (oprofile) Linux kernel module and notice that whole lot of cycles are spent in copy_from_user call. I compared same flow from kernel proper and noticed that for more data through put cycles spent in copy_from_user are much less. Kernel proper has 1/8 cycles compared to module. (There is a user process which keeps sending data, like iperf) Used perf tool to gather some statistics and found that call from kernel proper 185,719,857,837 cpu-cycles # 3.318 GHz [90.01%] 99,886,030,243 instructions # 0.54 insns per cycle [95.00%] 1,696,072,702 cache-references # 30.297 M/sec [94.99%] 786,929,244 cache-misses # 46.397 % of all cache refs [95.00%] 16,867,747,688 branch-instructions # 301.307 M/sec [95.03%] 86,752,646 branch-misses # 0.51% of all branches [95.00%] 5,482,768,332 bus-cycles # 97.938 M/sec [20.08%] 55967.269801 cpu-clock 55981.842225 task-clock # 0.933 CPUs utilized and call from kernel module 9,388,787,678 cpu-cycles # 1.527 GHz [89.77%] 1,706,203,221 instructions # 0.18 insns per cycle [94.59%] 551,010,961 cache-references # 89.588 M/sec [94.73%] 369,632,492 cache-misses # 67.083 % of all cache refs [95.18%] 291,358,658 branch-instructions # 47.372 M/sec [94.68%] 10,291,678 branch-misses # 3.53% of all branches [95.01%] 582,651,999 bus-cycles # 94.733 M/sec [20.55%] 6112.471585 cpu-clock 6150.490210 task-clock # 0.102 CPUs utilized 367 page-faults # 0.000 M/sec 367 minor-faults # 0.000 M/sec 0 major-faults # 0.000 M/sec 25,770 context-switches # 0.004 M/sec 23 cpu-migrations # 0.000 M/sec So obviously, CPU is stalling when it is copying data and there are more cache misses. My question is, is there a difference calling copy_from_user from kernel proper compared to calling from LKM ?

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[RFC]confusions about 'struct' define
by harryxiyou June 4, 2012

June 4, 2012

Hi guys, When I read the linux/device.h file for some device driver usage, i find some confusions like following. $ head -60 device.h [...] struct device; struct device_private; struct device_driver; struct driver_private; struct module; struct class; struct subsys_private; struct bus_type; struct device_node; struct iommu_ops; struct bus_attribute { struct attribute attr; ssize_t (*show)(struct bus_type *bus, char *buf); ssize_t (*store)(struct bus_type *bus, const char *buf, size_t count); }; [...] I have never seen struct define like "struct device; struct device_private; struct device_driver; [...] struct device_node; struct iommu_ops;" The common define is like this "struct a{ int a; int b; [...] }" Is this just struct declaration or some extension about gcc? Cloud anyone give me some explanations? Thanks in advance ;-) Note: my kernel version is 3.0 around. -- Thanks Harry Wei

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Faking SD-Card insertion/removel
by sougata santra June 1, 2012

June 1, 2012

I am new to linux device-drivers. I am trying to fake add, remove sd cards while they are mounted. For systems where sd card controller is connected to PCI bus. I can use fakephp to remove the controller itself. Can similar thing be done with "mmc" bus_type. So that I can fake card addition and removal. The current version of fakephp does not use anything from pci-hotplug subsystem. Is something similar possible ?. Thank you in advance. Best regards, Sougata.

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Re: cache policy of arm mmu
by h.t.jacky＠gmail.com June 1, 2012

June 1, 2012

Hi Cunsuo, Thanks for you prompt reply. But I'm just wondering why the other policies(such as writethrough) are abandoned, does anyone know the architecture difference? Cheers, Jacky Sent from my HTC ----- Reply message ----- From: "Cunsuo Guo" <cunsuo.guo(a)gmail.com> To: "Jacky lin" <h.t.jacky(a)gmail.com> Cc: <kernelnewbies(a)kernelnewbies.org> Subject: cache policy of arm mmu Date: Tue, May 29, 2012 09:10 Hi Jacky， I think the information of printk has already tell us the reason. 2012/5/29 Jacky lin <h.t.jacky(a)gmail.com>: > Hi all, > > I found that the cache policy in after ARMv6 is always set as writeback mode > in mmu.c. > > static int __init early_cachepolicy(char *p) > { > ... > if (cpu_architecture() >= CPU_ARCH_ARMv6) { > printk(KERN_WARNING "Only cachepolicy=writeback supported on ARMv6 > and later\n"); > cachepolicy = CPOLICY_WRITEBACK; > } > ... > } > > Does anyone know why and provide some documents or links for that? > > Thanks so much! > > Cheers, > Jacky > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >

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TWD, MCT, MSM timer
by naveen yadav May 31, 2012

May 31, 2012

Dear All, I want to know details about TWD, MCT, MSM timer. can any body let me know. Thanks

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task struct and the #! operator
by Ranjan Sinha May 31, 2012

May 31, 2012

Hi, I am trying to understand process creation and associated bookkeeping.I am currently trying to understand how interpreted scripts (the shebang operator) are executed. It was surprising to see that the comm member of task_struct (accessed through get_task_comm) is actually set to the name of the script though /proc/pid/exe correctly points to the invoked interpreter. Does anybody know where the necessary magic happen and is it possible to get the name of invoked interpreter through any means inside the kernel? Thanks in advance, Ranjan

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