shared memory problem on ARM v5TE using threads
Joerg Wagner
Joerg.Wagner at nw.neclab.eu
Fri Dec 4 07:26:46 EST 2009
Could you elaborate what you are expecting to see?
You are "read-modify-write"'ing a shared location without using atomic instructions, so it seems reasonable that the updates of the entry->in_msg are not behaving like you want them to behave.
Joerg
> -----Original Message-----
> From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-arm-
> kernel-bounces at lists.infradead.org] On Behalf Of Heiko Schocher
> Sent: Freitag, 4. Dezember 2009 12:24
> To: linux-arm-kernel at lists.infradead.org
> Subject: shared memory problem on ARM v5TE using threads
>
> Hello,
>
> I have the following shared mem problem on a ARM v5TE
> processor using Linux version 2.6.28,
>
> -bash-3.2# cat /proc/cpuinfo
> Processor : Feroceon 88FR131 rev 1 (v5l)
> BogoMIPS : 799.53
> Features : swp half thumb fastmult edsp
> CPU implementer : 0x56
> CPU architecture: 5TE
> CPU variant : 0x2
> CPU part : 0x131
> CPU revision : 1
>
> The testscript [1] starts 2 processes. One write
> process with one thread, which writes in a shared memory.
>
> The second process starts 4 threads, which all read from
> this shared memory. This don;t work on this processor [4].
> The same demoprogramm works fine on ppc, i386 or on a
> ARMv6 based board [3][6] ...
>
> If I start 4 read processes, which themselves starts only
> one readthread [5], the demoprogramm works fine!
>
> Also, if I start one read process, which only attaches
> the shared memory once with shmat(), and then starts 4
> read threads, and all this 4 read threads using
> the same shared memory addr, returned from shmat(),
> this works as expected.
>
> Any ideas, hints ... ?
>
> TIA
>
> bye,
> Heiko
> --
> DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
>
>
> [1] Testscript
>
> #!/bin/sh
> echo "Compile"
> gcc -o shmtest2 shmtest2.c -lpthread
>
> echo "Run shmtest2"
> ./shmtest2 write 1 &
> ./shmtest2 read 4 &
>
>
> [2] demoprogramm, shmtest2.c
>
> #include <pthread.h>
> #include <sys/types.h>
> #include <sys/ipc.h>
> #include <sys/shm.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <string.h>
>
> extern void exit();
>
> struct Entry
> {
> char ident_name[1000];
> unsigned int tipc_nr;
> unsigned int pid;
> unsigned int in_msg;
> unsigned int out_msg;
> unsigned int rxQueueLength;
> };
>
> void* attachSharedMem(int shmid)
> {
> void* addr = shmat(shmid, NULL, 0);
> if ((addr != 0) && (0xffffffff != (unsigned int)addr))
> {
> printf("attach shared mem:%x\n",addr);
> }
> else
> {
> printf("shmat failed");
> addr = 0;
> }
> return addr;
> }
>
> int createSharedMem()
> {
> key_t key = 1000; /* 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() */
>
> size = 60000;
> shmflg = IPC_CREAT | 0666;
> if ((shmid = shmget (key, size, shmflg)) == -1)
> {
> printf("shmget failed");
> shmid = 0;
> }
>
> printf("Shared memory Id:%d\n",shmid);
>
> return shmid;
> }
>
>
> void* setupSharedMem()
> {
> int shmid = createSharedMem();
> void* addrShm = attachSharedMem(shmid);
> return addrShm;
> }
>
> void *readThread(void *t)
> {
> struct Entry* entry = 0;
>
> int shmid = (int)t;
> void* addrShm = attachSharedMem(shmid);
>
> if (addrShm != 0)
> {
> printf("Start Read Thread addr:%x\n",addrShm);
> entry = (struct Entry*)addrShm;
> entry->in_msg = 0;
> entry->out_msg = 0;
>
> int i=0;
> while(i < 60)
> {
> entry->in_msg += 1000;
> sleep(1);
> printf("Read from entry in_msg=%d, out_msg=%d, addr=%x\n",entry-
> >in_msg,entry->out_msg, addrShm);
> i++;
> }
> }
>
> pthread_exit(NULL);
> }
>
> void *writeThread(void *t)
> {
> struct Entry* entry = 0;
> unsigned int threadId = (unsigned int)t;
> void* addrShm = setupSharedMem();
>
> if (addrShm != 0)
> {
> printf("Start Write Thread %d, addr:%x\n",threadId,addrShm);
> entry = (struct Entry*)addrShm;
> strcpy(entry->ident_name,"this is a test entry");
> entry->in_msg = 0;
> entry->out_msg = 0;
> entry->rxQueueLength = 20000;
> entry->pid = threadId;
> entry->tipc_nr = 1000;
>
> int i=0;
> while(i < 60)
> {
> entry->out_msg += 1000;
> sleep(1);
> i++;
> }
> }
>
> pthread_exit(NULL);
> }
>
> main(int argc, char* argv[])
> {
>
> //check the arguments
> if (argc != 3)
> {
> printf("Arguments are [read|write] [number of threads]\n");
> exit(1);
> }
>
> unsigned int mode = 0;
> unsigned int nbrOfThreads = 0;
>
> if (strcmp(argv[1],"write") == 0)
> {
> printf("Write to in_msg\n");
> mode = 1;
> }
>
> if (strcmp(argv[1],"read") == 0)
> {
> printf("Read from in_msg\n");
> mode = 2;
> }
>
> nbrOfThreads = atoi(argv[2]);
>
> pthread_t threads[nbrOfThreads];
> pthread_attr_t attr;
>
> /* Initialize and set thread detached attribute */
> pthread_attr_init(&attr);
> pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
>
> unsigned int t;
> int rc;
> for(t=0; t<nbrOfThreads; t++)
> {
> printf("Creating thread %ld\n", t);
> if (mode == 1)
> {
> rc = pthread_create(&threads[t], &attr, writeThread, (void
> *)t);
> }
> else
> {
> int shmid = createSharedMem(t);
> rc = pthread_create(&threads[t], &attr, readThread, (void
> *)shmid);
> }
>
> if (rc)
> {
> printf("ERROR; return code from pthread_create() is %d\n", rc);
> exit(-1);
> }
> }
>
> void* status;
> pthread_attr_destroy(&attr);
> for(t=0; t<nbrOfThreads; t++)
> {
> pthread_join(threads[t], &status);
> }
>
> printf("All %s threads finished, exit\n",mode == 1 ?
> "write":"read");
>
> exit(0);
> }
>
> [3] ARMv6 processor cpuinfo
> -bash-3.2# cat /proc/version
> Linux version 2.6.32-rc6 (dzu at pollux.denx.de) (gcc version 4.2.2) #4
> Thu Dec 3 12:31:13 CET 2009
> -bash-3.2# cat /proc/cpuinfo
> Processor : ARMv6-compatible processor rev 4 (v6l)
> BogoMIPS : 398.13
> Features : swp half thumb fastmult vfp edsp java
> CPU implementer : 0x41
> CPU architecture: 6TEJ
> CPU variant : 0x0
> CPU part : 0xb36
> CPU revision : 4
>
> [4] Log from Demoprogramm, not working
>
> -bash-3.2# ./shtest2.sh
> Run shmtest2
> Read from in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40961000
> Start Read Thread addr:40961000
> Write to in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40961000
> Start Write Thread 0, addr:40961000
> 348: write new mesg: 0
> Read from in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40961000
> Start Read Thread addr:40961000
> Creating thread 1
> Shared memory Id:0
> Read from in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40961000
> Start Read Thread addr:40961000
> attach shared mem:41170000
> Start Read Thread addr:41170000
> Read from in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40961000
> Start Read Thread addr:40961000
> -bash-3.2# Read from entry in_msg=1000, out_msg=0, addr=40961000
> Read from entry in_msg=0, out_msg=0, addr=40961000
> Read from entry in_msg=2000, out_msg=1000, addr=40961000
> Read from entry in_msg=1000, out_msg=0, addr=41170000
> Read from entry in_msg=3000, out_msg=1000, addr=40961000
> Read from entry in_msg=4000, out_msg=1000, addr=40961000
> Read from entry in_msg=2000, out_msg=0, addr=40961000
> Read from entry in_msg=5000, out_msg=2000, addr=40961000
> Read from entry in_msg=3000, out_msg=0, addr=41170000
> Read from entry in_msg=6000, out_msg=2000, addr=40961000
> Read from entry in_msg=7000, out_msg=2000, addr=40961000
> Read from entry in_msg=4000, out_msg=0, addr=40961000
> Read from entry in_msg=8000, out_msg=3000, addr=40961000
> Read from entry in_msg=5000, out_msg=0, addr=41170000
> Read from entry in_msg=9000, out_msg=3000, addr=40961000
> Read from entry in_msg=10000, out_msg=3000, addr=40961000
> [...]
>
> [5] Testscript which starts 4 read processes each with
> one read thread
>
> #!/bin/sh
> echo "Compile"
> gcc -o shmtest2 shmtest2.c -lpthread
>
> echo "Run shmtest2"
> ./shmtest2 write 1 &
> ./shmtest2 read 1 &
> ./shmtest2 read 1 &
> ./shmtest2 read 1 &
> ./shmtest2 read 1 &
>
> [6] working log on ARMv6
>
> -bash-3.2# ./shtest2.sh
> Run shmtest2
> Write to in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40960000
> Start Write Thread 0, addr:40960000
> Read from in_msg
> Creating thread 0
> Shared memory Id:0
> attach shared mem:40960000
> Start Read Thread addr:40960000
> Creating thread 1
> Shared memory Id:0
> Creating thread 2
> Shared memory Id:0
> Creating thread 3
> Shared memory Id:0
> attach shared mem:4216f000
> Start Read Thread addr:4216f000
> attach shared mem:4217e000
> Start Read Thread addr:4217e000
> attach shared mem:4218d000
> Start Read Thread addr:4218d000
> -bash-3.2# Read from entry in_msg=1000, out_msg=1000, addr=40960000
> Read from entry in_msg=2000, out_msg=1000, addr=4216f000
> Read from entry in_msg=3000, out_msg=1000, addr=4217e000
> Read from entry in_msg=4000, out_msg=1000, addr=4218d000
> Read from entry in_msg=5000, out_msg=2000, addr=40960000
> Read from entry in_msg=6000, out_msg=2000, addr=4216f000
> Read from entry in_msg=7000, out_msg=2000, addr=4217e000
> Read from entry in_msg=8000, out_msg=2000, addr=4218d000
> Read from entry in_msg=9000, out_msg=3000, addr=40960000
> Read from entry in_msg=10000, out_msg=3000, addr=4216f000
> Read from entry in_msg=11000, out_msg=3000, addr=4217e000
> Read from entry in_msg=12000, out_msg=3000, addr=4218d000
> Read from entry in_msg=13000, out_msg=4000, addr=40960000
> Read from entry in_msg=14000, out_msg=4000, addr=4216f000
> Read from entry in_msg=15000, out_msg=4000, addr=4217e000
> Read from entry in_msg=16000, out_msg=4000, addr=4218d000
> [...]
>
>
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