Poor performance when multi-processes write one msg on linux - c

Question

Ｉ write a test program as follows:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/msg.h>
#include <time.h>
#define PACKET_SIZE 500
#define LOOP_COUNT 30000
int g_sndsucc = 0;
int g_sndfail = 0;
const int C_IPC_KEY = 0x00231a95;
const int COUNT_SIZE = 10000;
unsigned long g_count = 0;
unsigned long g_t1 = 0;
struct timeval s1, s2, s3, s4;
int main(int argc, char* argv[])
{
int ipckey = C_IPC_KEY;
if(argc > 1)
{
ipckey = atoi(argv[1]);
printf("ipckey is %d\n", ipckey);
}
int qid = msgget(ipckey, IPC_CREAT | 0666);
if(qid <= 0)
{
printf("msgget err: %d \n", errno);
return 0;
}
char data[PACKET_SIZE];
memset(data, 'a', PACKET_SIZE-1);
data[PACKET_SIZE-1] = '\0';
*((long *)data) = 0;
int ret = 0;
struct timeval start;
gettimeofday (&start, NULL);
while(1)
{
*((long *)data) +=1;
gettimeofday (&s1, NULL);
ret = msgsnd(qid, data, PACKET_SIZE,0);
gettimeofday (&s2, NULL);
if(ret != 0)
{
g_sndfail ++;
}
else
{
g_sndsucc ++;
}
g_count++;
g_t1 += (s2.tv_sec-s1.tv_sec)*1000000 + (s2.tv_usec-s1.tv_usec);
if ( g_count >= 10000)
{
printf("STAT1: t1 : %f\n",
10000000000.0 / g_t1);
g_count = 0;
g_t1 = 0;
}
usleep(1000);
}
return 0;
}
I create 100 same processes to msgsnd , and on suse, each process's msgsnd tps only reaches 50/s.
But on AIX5 the msgsnd tps can reaches 10000/s.
Does anyone know why the performance of IPC on linux when multi-processes is so poor?
And how to increase the performance on linux??
BTW, the kenel version of suse is linux 3.0.13

Answer 1

I checked the source code of the msgget in linux3.8.
When the thread did not get the msg lock, it is not release cpu and sleep some time.
Instead it will call ipc_lock_by_ptr(&msq->q_perm); frequently.
So the cpu usage will be very high, and the collision rate will grow rapidly when the threads increas.