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>12.2. My processes won't migrate</H1
><P
><EM
>Help process XYZ doesn't migrate. </EM
>
Moshe Bar explains below why some processes migrate and why some don't.
But before that you can always look in /proc/$pid/, there often is a
<EM
>cantmove</EM
> file which will tell you why a certain
process can't migrate.</P
><P
>Processes can also be locked.
You can check if a process is locked with:
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>cat /proc/$PID/lock</PRE
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>
where $PID is the processid of the process in question. </P
><P
>Now listen to what Moshe himself has to say about this
topic. </P
><P
>Often people have the same kernel but on a different
distribution, say a mixed environment of RedHat and Debian ,rc
scripts from different distros tend to start openmosix
differently. Some implementations completely modify
/etc/inittab to start all daemons (and their children) with
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>mosrun -h</PRE
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>. So that they won't migrate.
Therefore all these processes have a 1 in
/proc/pid/lock when you start. You can force them to migrate
by writing a 0 to this file .</P
><P
>
Ok, this simple program should always migrate if launched more times than
number of local CPUs. So for a 2-way SMP system, starting this program 3
times will start migration if the other nodes in the cluster have at least
the same speed like the local ones:
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><PRE
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>int main() {
unsigned int i;
while (1) {
i++;
}
return 0;
}</PRE
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>
On a Pentium 800Mhz CPU it takes quite a while to overflow. </P
><P
>
This sample program with content like this will never migrate:
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><PRE
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>#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
...
key_t key; /* key to be passed to shmget() */
int shmflg; /* shmflg to be passed to shmget() */
int shmid; /* return value from shmget() */
int size; /* size to be passed to shmget() */
...
key = ...
size = ...
shmflg) = ...
if ((shmid = shmget (key, size, shmflg)) == -1) {
perror("shmget: shmget failed"); exit(1); } else {
(void) fprintf(stderr, "shmget: shmget returned %d\n", shmid);
exit(0);
}
...</PRE
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> </P
><P
> Program using pipes like this do migrate nicely:
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> int pdes[2];
pipe(pdes);
if ( fork() == 0 )
{ /* child */
close(pdes[1]); /* not required */
read( pdes[0]); /* read from parent */
.....
}
else
{ close(pdes[0]); /* not required */
write( pdes[1]); /* write to child */
.....
}</PRE
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>
<EM
>MODIFIED</EM
>
Programs using pthreads since version 2.4.17 don't migrate, however they
don't segfault anymore.
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>//
// Very simple program demonstrating the use of threads.
//
// Command-line argument is P (number of threads).
//
// Each thread writes "hello" message to standard output, with
// no attempt to synchronize. Output will likely be garbled.
//
#include <iostream>
#include <cstdlib> // has exit(), etc.
#include <unistd.h> // has usleep()
#include <pthread.h> // has pthread_ routines
// declaration for function to be executed by each thread
void * printHello(void * threadArg);
// ---- Main program -------------------------------------------------
int main(int argc, char* argv[]) {
if (argc < 2) {
cerr << "Usage: " << argv[0] << " numThreads\n";
exit(EXIT_FAILURE);
}
int P = atoi(argv[1]);
// Set up IDs for threads (need a separate variable for each
// since they're shared among threads).
int * threadIDs = new int[P];
for (int i = 0; i < P; ++i)
threadIDs[i] = i;
// Start P new threads, each with different ID.
pthread_t * threads = new pthread_t[P];
for (int i = 0; i < P; ++i)
pthread_create(&threads[i], NULL, printHello,
(void *) &threadIDs[i]);
// Wait for all threads to complete.
for (int i = 0; i < P; ++i)
pthread_join(threads[i], NULL);
// Clean up and exit.
delete [] threadIDs;
delete [] threads;
cout << "That's all, folks!\n";
return EXIT_SUCCESS;
}
// ---- Code to be executed by each thread ---------------------------
// pre: *threadArg is an integer "thread ID".
// post: "hello" message printed to standard output.
// return value is null pointer.
void * printHello(void * threadArg) {
int * myID = (int *) threadArg;
cout << "hello, world, ";
// pointless pause, included to make the effects of
// synchronization (or lack thereof) more obvious
usleep(10);
cout << "from thread " << *myID << endl;
pthread_exit((void* ) NULL);
}
</PRE
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>
Programs using all kinds of file descriptors, including sockets do migrate
(sockets are not migrated with the process however, files are migrated if
using oMFS/DFSA)</P
><P
> (all above code is by Moshe as Moshe Bar or by Moshe as CTO of Qlusters, Inc.) </P
><P
>Please also refer to the man pages of openMosix , they also give an
adequate explanation why processes don't migrate. </P
><P
>If for some reason your processes stay locked while they shouldn't. You
can try to allow locked processes to migrate by simply putting
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># tell shells to allow subprocs to migrate to other nodes
echo 0 > /proc/self/lock</PRE
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>
into
<SPAN
CLASS="QUOTE"
>"/etc/profile"</SPAN
>
Warning : this fix will allow <EM
>all</EM
> process to migrate
not just the ones you want. To only allow specific process to migrate
use 'mosrun -l' to unlock only the desired process.
</P
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