Hello mysql,
Some time ago I wrote about slow down of mysql with large number of
threads, which is quite common in Linux-Apache-Mysql-PHP enviroment.
The test was simulating the worst case of concurrency - all the
threads are modified global variable in a loop 5000000 times in
total, using standard mutex for synchronization. The yeild is used
in a loop to force even more fair distribution of lock usage by
threads and increase context switches, therefore it did not change
much with large number of threads. I.e with 64 threads time without
yeild is 1:33.5
Test was run on PIII-500 1G RAM Kernel 2.4.18. 3 runs were made for
each number of threads and best results were taken:
Num threads. Time Peak cs rate.
2 53.4 179518
4 53.8 144828
16 1:06.3 85172
64 1:48.1 48394
256 8:10.6 10235
1000 36:46.2 2602
The surprising thing is the time grows in less then linear way for up
to 64 threads but later it stars to go linear way or even worse. May
be this is because some other process are sleeping in the system which
also is used in scheduling.
For Next test I'll try to use Ingo's scheduler to see if it helps to
solve the problem, also I'll try to test real mysql server to see
which slowdown it will have.
CODE: (Dumb one just for test)
#include <stdio.h>
#include <pthread.h>
#include <time.h>
#define NUM_TH 1000
#define TOTAL_VALUE 5000000
#define LOOP (TOTAL_VALUE/NUM_TH)
pthread_t th[NUM_TH];
int thread_data[NUM_TH];
int rc,rc2;
int global=0;
pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t start = PTHREAD_MUTEX_INITIALIZER;
void f(int *thn)
{
int i;
pthread_mutex_lock(&start);
pthread_mutex_unlock(&start);
for (i=0;i<LOOP;i++)
{
pthread_mutex_lock(&mut);
global++;
pthread_yield();
pthread_mutex_unlock(&mut);
}
}
main()
{
int i;
pthread_mutex_lock(&start);
for (i=0;i<NUM_TH;i++)
{
thread_data[i]=i;
rc=pthread_create(&th[i],NULL,f,&thread_data[i]);
if (rc!=0)
{
printf("Failed to create thread #%d errorcode:%d\n",i,rc);
}
}
pthread_mutex_unlock(&start);
for (i=0;i<NUM_TH;i++)
{
rc2=pthread_join(th[i],NULL);
}
printf("Global Value: %d\n",global);
}
-- Best regards, Peter mailto:pz@spylog.ru- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri Mar 15 2002 - 22:00:20 EST