February 2011 - kernelnewbies@kernelnewbies.org

Thread Affinity structure
by Sri Ram Vemulpali Feb. 5, 2011

Feb. 5, 2011

Hi all, I have doubt regarding how the thread affinity (to processor) is defined in a process (task). If there is only single thread in a process, then when process calls itself on binding to a core, will let run on that core forever. But, what if there are multiple threads, in a process (task). If the main thread calls set affinity to a core, is it going to get inherited to all other threads, or just the calling thread in a task. What happens when forked a process with threads that has affinity to a core. Please can anyone point me to the literature on this. Thanks in advance. -- Regards, Sri.

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Re: page size change on MIPS
by naveen yadav Feb. 5, 2011

Feb. 5, 2011

thanaks a lot for your suggestion .. I debug this issue further, and here is my observations: 1. If I replace init with simple static link executable binary, this can be executed. 2. In case of busy-box, I debug the reason why init fails to excute. When I execute init command from busybox the control goes in main() function of busybox(appletlib.c) with argv value as the command you are suppose to execute, which in our case is init. But when i check argv is coming null when page size is 64KB and it comes init when page size is 16KB. This behaviour is very strange and i am still debugging this issue. I have check in Glibc, the max_page size it support is 64 KB in codesourcercy toolchain 4.4.1 How can I check alignment issue as mention by Mr. Ralf Baechle. Kind regards On Mon, Jan 31, 2011 at 6:38 PM, Ralf Baechle <ralf(a)linux-mips.org> wrote: > On Sun, Jan 30, 2011 at 08:32:43PM +0530, Himanshu Aggarwal wrote: > >> Why should the application or the toolchains depend on pagesize? I am >> not very clear on this. Can someone explain it? > > To allow loading directly with mmap the executable file's layout must > be such that it's it's segments are on offsets that are a multiple of > the page size so in turn the linker must know that alignment. > > Ralf >

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Re: Thread Affinity structure
by Sri Ram Vemulpali Feb. 4, 2011

Feb. 4, 2011

Hi Christoph, Thanks for response. Can you please explain in little bit elaborate what do you mean "The value returned from a call to gettid(2) can be passed in the argument pid. Specifying pid as 0 will set the attribute for the calling thread, and passing the value returned from a call to getpid(2) will set the attribute for the main thread of the thread group." To whom I should pass the id. I did not understood. Thanks, Sri. On Fri, Feb 4, 2011 at 2:29 PM, Christoph Lameter <cl(a)linux.com> wrote: > On Fri, 4 Feb 2011, Sri Ram Vemulpali wrote: > >> I have doubt regarding how the thread affinity (to processor) is >> defined in a process (task). If there is only single thread in a >> process, then when process calls itself on binding to a core, will let >> run on that core forever. But, what if there are multiple threads, in >> a process (task). If the main thread calls set affinity to a core, is >> it going to get inherited to all other threads, or just the calling >> thread in a task. What happens when forked a process with threads that >> has affinity to a core. Please can anyone point me to the literature >> on this. Thanks in advance. > > See "man sched_setaffinity" > > " > The affinity mask is actually a per-thread attribute that can be > adjusted independently for each of the threads in a thread group. The > value returned from a call to gettid(2) can be passed in the argument > pid. Specifying pid as 0 will set the attribute for the calling thread, > and passing the value returned from a call to getpid(2) will set the > attribute for the main thread of the thread group. (If you are using > the POSIX threads API, then use pthread_setaffinity_np(3) instead of > sched_setaffinity().) > " > > > > The setting of the affinity occurs for the running thread if pid == 0. > Affinity masks are inherited across forks. > > > > > > -- Regards, Sri.

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Regarding PREEMPT_RT option
by Sri Ram Vemulpali Feb. 3, 2011

Feb. 3, 2011

Hi all, I am trying to find detailed explanation of preemption option in config. For desktop, server, and low-latency desktop. Can anyone explain in what scenarios these are useful. Thanks in advance -- Regards, Sri.

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x86 memory detection
by Arun S Feb. 3, 2011

Feb. 3, 2011

Hi, How does the kernel detects the amount of available System RAM in the system under x86 architecture?. Under 2.6.x kernels, 1. Does it use BIOS interrupt 15 for determining the RAM OR 2. Does the boot loader fills the e820_map as explained inDocumentation/x86/boot.txt & Documentation/x86/zero-page.txt and the kernel uses in information OR 3. Is there any other mechanism (if so, in which file under kernel tree I can find this detection code) Thanks, Arun

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how to give su permissions to debugging console
by Pradeep Kumar Feb. 3, 2011

Feb. 3, 2011

hi all, I'm using serial console uart as debugging console. I have enabled command line with CONFIG_CMDLINE="console=ttyS0,115200n8" config. console is coming up but I'm unable to get su permissions by default. am I missing something??? -- Goudagunta Pradeep Kumar,

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Asking advice for graduate study
by cheng chen Feb. 2, 2011

Feb. 2, 2011

Hi, all! I am going to further my education in graduate school of Master of Science degree. I am interested in network, but I am not sure what direction I should choose and which professional books I should read. Therefore I ask for help and suggestion from you. In summary, I have both the fundamental knowledge about network programming as well as communication theory. Therefore I prefer an area which has the relationship with both the software and hardware (but with more attention on software.) By the way, I am especially interested in how the whole network system works, rather than how two single points communicate. If you have any suggestion about what I could do next (areas, books, whaever~), please be kind to tell me. Thank you very much. -- Cheng(誠) Fedora Project Contributor -- Ambassador https://fedoraproject.org/wiki/User:Freakrobot _______________________________________________ My Page: http://freakrobot.blogbus.com/

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Regarding SIGSEGV
by Sri Ram Vemulpali Feb. 2, 2011

Feb. 2, 2011

Hi all, I know that when a thread in an application do invalid memory reference, OS generates SIGSEGV(segmentation fault) signal and terminates application. What if we handle this signal by defining a signal handler to perform to terminate only the thread did invalid memory reference. So, that the application will not be terminated. Also, is there any way, we can find when SIGSEGV is generated to get the invalid memory reference and thread id, who caused this fault. I know debuggers are written in such fashion. Can anyone point me to right direction. Thanks in advance. -- Regards, Sri.

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avoid ip forward replaces the source MAC address
by Elvis Yoan Tamayo Mollares Feb. 2, 2011

Feb. 2, 2011

hi list, during ip forwarding process, the kernel replace the source MAC address of the package it received with my own MAC address.. My question is: Is there any way to avoid this behavior? Regards.

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ARM Cross Compilation Toolchain on x86 machine
by Madhavi Manchala Feb. 1, 2011

Feb. 1, 2011

Dear All, We are unable to build the ARM cross compilation tools for arm-elf-gcc-3.4.3 on my x86 machine on which we installed the Ubuntu 9.10 distribution OS with 2.6.35 kernel version. The gcc version on x86 machine is 4.3.3. We need to compile some sources on my x86 machine for our target machine which is based on ARM architecture. We have gone through following links to build the cross compilation tools for arm-elf-gcc 3.4.3 on my x86 machine. http://www.ailis.de/~k/archives/19-ARM-cross-compiling-howto.html http://www.kegel.com/crosstool/current/doc/crosstool-howto.html http://www.kegel.com/crosstool/ Unfortunately we end up with different types of errors. When we fix one error then we get another new error. We tried in different ways to build the tools on my x86 machine. There is no luck at all. We also gone through the http://www.gnuarm.com/ site and downloaded the binaries for gcc 3.4. toolchain. However, we did not find any README for how to use these binaries. Please let us know if there is any clean procedure/document/link for building/using the arm-elf-gcc 3.4.3 toolchain on my x86 machine. Any help would be greatly appreciated and help us a lot. Thanks and Regards, Madhavi M.

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