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Search found 64 results on 3 pages for 'osgx'.

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  • Programmatically measure size and way-order of L1 and L2 caches

    - by osgx
    How can I measure programmatically (not query the OS, but measure) the size and order of associativity of L1 and L2 caches (data caches)? Assumptions about system: It has L1 and L2 cache (may be L3 too, may be cache sharing), It may have a hardware prefetch unit (just like P4+), It has a stable clocksource (tickcounter or good HPET for gettimeofday). There are no assumptions about OS (it can be Linux, Windows, or something non-standard), and we can't use POSIX queries. Language is C. And compiler optimizations may be disabled.

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  • MPI: is there mpi libraries capable of message compression?

    - by osgx
    Sometimes MPI is used to send low-entropy data in messages. So it can be useful to try to compress messages before sending it. I know that MPI can work on very fast networks (10 Gbit/s and more), but many MPI programs are used with cheap network like 0,1G or 1Gbit/s Ethernet and with cheap (slow, low bisection) network switch. There is a very fast Snappy (wikipedia) compression algorithm, which has Compression speed is 250 MB/s and decompression speed is 500 MB/s so on compressible data and slow network it will give some speedup. Is there any MPI library which can compress MPI messages (at layer of MPI; not the compression of ip packets like in PPP). MPI messages are also structured, so there can be some special method, like compression of exponent part in array of double.

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  • Automatic translation from fortran 90 to f77

    - by osgx
    Hello Is there an converter from fortran 90 downto fortran 77 ? I have a fortran77 only compiler and want to run NAS Parallel Benchmark (NPB for short) on it. But NPB uses some features of F90, like do enddo, smth else. All features are rather simple. Is there A way to translate NPB to F77 strict language? Tags: fortran parallel convert programming-languages

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  • barriers in SMP linux kernel

    - by osgx
    Hello Is there smth like pthread_barrier in SMP Linux kernel? When kernel works simultaneously on 2 and more CPUs with the same structure, the barrier (like pthread_barrier) can be useful. It will stop all CPUs entering to it until last CPU will run the barrier. From this moment all CPUs again works.

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  • Programicaly measure size and way-order of L1 and L2 caches

    - by osgx
    Hello How can I measure programicaly (not query the OS, but measure) the size and order of associativity of L1 and L2 caches (data caches)? Assumtions about system: It has L1 and L2 cache (may be L3 too, may be cache sharing), It may have a hardware prefetch unit (just like P4+), it has a stable clocksource (tickcounter or good HPET for gettimeofday). There are no assumtions about OS (it can be Linux, Windows, smth non-standart), and we can't use posix queries. Language is C. And Compiler optimizations may be disabled.

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  • Sources of latency in sending-receiving tcp/udp packets in linux

    - by osgx
    Hello What are sources of latency in process of sending/receiving tcp/udp packets in linux 2.6 ? I want to know a latency sources in "ping-pong" latency tests. There are some rather good papers of ethernet latency, but they cover only latency sources in the wire and switch (and rather cursory, only for specific switch). What steps of processing does follow a packet? Papers with deep latency analysis of usual ping (icmp) will be useful too. I rely on community :)

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  • Manage a `visited` links history in browsers

    - by osgx
    Hello Can I edit the browser's visited links history? How can I dump full list of visited sites, or list of pages from some site? I'm interested in the solution for the most popular browsers: IE7-8, Firefox3, Safari4, Chrome3, Opera9.50+ The best will be solution, which can be scripted in JS+CSS. But plugins or instructions for managing visited links history will be good. Thanks

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  • How can I get page faults statistics from kernel

    - by osgx
    Hello How can I get page faults statistics from kernel for my application while it is running? What about other events, like inter-cpu migrations count in SMP nodes, or number of context switches? I want to count such events for various small parts of the program. Thanks.

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  • ptrace'ing of parent process

    - by osgx
    Hello Can child process use the ptrace system call to trace its parent? Os is linux 2.6 Thanks. upd1: I want to trace process1 from "itself". It is impossible, so I do fork and try to do ptrace(process1_pid, PTRACE_ATTACH) from child process. But I can't, there is a strange error, like kernel prohibits child from tracing their parent processes UPD2: such tracing can be prohibited by security policies. Which polices do this? Where is the checking code in the kernel? UPD3: on my embedded linux I have no errors with PEEKDATA, but not with GETREGS: child: getregs parent: -1 errno is 1, strerror is Operation not permitted errno = EPERM

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  • detect sender of signal (linux, ptrace)

    - by osgx
    Hello Can I distinguish signal, between delivered directly to a process and delivered via debugger. Case 1: $ ./process1 process1 (not ptraced) set up handler alarm(5); .... signal is handled and I can parse handler parameters Case 2: $ debugger1 ./process1 process1 (is ptraced by debugger1) set up handler alarm(5); ... signal is catched by debugger1. It resumes process1 with PTRACE_CONT, signal_number is 4th parameter of PTRACE_CONT. signal is redelivered to process1 it is handled. So, how can I detect in signal handler, was it redelivered by debugger or send by system? OS is Linux, kernel is 2.6.30. Programs are written in plain C.

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  • Using objects with STL vector - minimal set of methods

    - by osgx
    Hello What is "minimal framework" (necessary methods) of object, which I will use with STL <vector>? For my assumptions: #include <vector> #include <cstring> using namespace std; class Doit { private: char *a; public: Doit(){a=(char*)malloc(10);} ~Doit(){free(a);} }; int main(){ vector<Doit> v(10); } gives *** glibc detected *** ./a.out: double free or corruption (fasttop): 0x0804b008 *** Aborted and in valgrind: malloc/free: 2 allocs, 12 frees, 50 bytes allocated.

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  • How to migrate existing udp application to raw sockets

    - by osgx
    Hello Is there a tutorial for migration from plain udp sockets (linux, C99/C++, recv syscall is used) to the raw sockets? According to http://aschauf.landshut.org/fh/linux/udp_vs_raw/ch03s04.html raw socket is much faster than udp. Application is client-server. client is proprietary and must use exactly same procotol as it was with udp server. But server can be a bit faster with raw sockets. What parts of udp I must to implement in server? Is there a "quick migration" libraries?

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  • tracing a linux kernel, function-by function (biggest only) with us timer

    - by osgx
    Hello I want to know, how does the linux kernel do some stuff (receiving a tcp packet). In what order main tcp functions are called. I want to see both interrupt handler (top half), bottom half and even work done by kernel after user calls "read()". How can I get a function trace from kernel with some linear time scale? I want to get a trace from single packet, not the profile of kernel when receiving 1000th of packets. Kernel is 2.6.18 or 2.6.23 (supported in my debian). I can add some patches to it.

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  • data path (travel) of tcp data from "write" syscall downto I/O registers programming

    - by osgx
    Hello Is there a good overview of tcp data path in Linux (2.6, not 2.4 if the path actually differ)? Where is a packet on different stages of tcp/ip stack handling? How packet is packed to tcp segment, then ip packet. How it is transmitted to network card? (with series of I/O regs write and DMA?) Is it transmitted to network card in the "write" syscall handler (with some deep callstack) or is it transmitted at some other moment?

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  • one two-directed tcp socket OR two one-directed? (linux, high volume, low latency)

    - by osgx
    Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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  • one two-directed tcp socket of two one-directed? (linux, high volume, low latency)

    - by osgx
    Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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  • pthread functions "_np" suffix

    - by osgx
    What does "_np" suffix mean here: pthread_mutex_timedlock_np or in macros PTHREAD_MUTEX_TIMED_NP Upd: From glibc2.2 enum { PTHREAD_MUTEX_TIMED_NP, PTHREAD_MUTEX_RECURSIVE_NP, PTHREAD_MUTEX_ERRORCHECK_NP, PTHREAD_MUTEX_ADAPTIVE_NP #ifdef __USE_UNIX98 , PTHREAD_MUTEX_NORMAL = PTHREAD_MUTEX_TIMED_NP, PTHREAD_MUTEX_RECURSIVE = PTHREAD_MUTEX_RECURSIVE_NP, PTHREAD_MUTEX_ERRORCHECK = PTHREAD_MUTEX_ERRORCHECK_NP, PTHREAD_MUTEX_DEFAULT = PTHREAD_MUTEX_NORMAL #endif #ifdef __USE_GNU /* For compatibility. */ , PTHREAD_MUTEX_FAST_NP = PTHREAD_MUTEX_ADAPTIVE_NP #endif }; Does defining __USE_UNIX98 change portability of _NP functions/macro?

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  • Small openmp programm freezes sometimes (gcc, c, linux)

    - by osgx
    Hello Just write a small omp test, and it does not work correctly all the times: #include <omp.h> int main() { int i,j=0; #pragma omp parallel for(i=0;i<1000;i++) { #pragma omp barrier j+= j^i; } return j; } The usage of j for writing from all threads is incorrect in this example, BUT there must be only nondeterministic value of j I have a freeze. Compiled with gcc-4.3.1 -fopenmp a.c -o gcc -static Run on 4-core x86_Core2 Linux server: $ ./gcc and got freeze (sometimes; like 1 freeze for 4-5 fast runs). Strace: [pid 13118] <... futex resumed> ) = 0 [pid 13118] futex(0x80d3014, FUTEX_WAIT, 2, NULL <unfinished ...> [pid 13120] <... futex resumed> ) = 0 [pid 13119] futex(0x80d3014, FUTEX_WAIT, 2, NULL <unfinished ...> [pid 13120] futex(0x80d3014, FUTEX_WAKE, 1) = 1 [pid 13120] futex(0x80cd798, FUTEX_WAIT, 1, NULL <unfinished ...> [pid 13109] <... futex resumed> ) = 0 [pid 13109] futex(0x80d3014, FUTEX_WAKE, 1) = 1 [pid 13109] futex(0x80d3020, FUTEX_WAIT, 251, NULL <unfinished ...> [pid 13118] <... futex resumed> ) = 0 [pid 13118] futex(0x80d3014, FUTEX_WAKE, 1) = 1 [pid 13119] <... futex resumed> ) = 0 [pid 13118] futex(0x80d3020, FUTEX_WAIT, 251, NULL <unfinished ...> [pid 13119] futex(0x80d3014, FUTEX_WAKE, 1) = 0 [pid 13119] futex(0x80d3020, FUTEX_WAIT, 251, NULL <freeze> Why do I have a freeze (deadlock)?

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