Bruce Cran wrote:
On Thu, 10 Sep 2009 20:57:32 -0400
Pierre-Luc Drouin <[email protected]> wrote:
Hi,
I have an overclocked i7 920 CPU for which I have enabled Turbo Mode
in the BIOS (21x multiplier). The base clock is set at 190 MHz, so
the CPU frequency with Turbo mode activated should be 3990 MHz.
However the maximum value FreeBSD amd64 shows for the CPU frequency
in dmesg and sysctl is 3790 MHz. How can I enable the Turbo Mode?
CPU: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz (3790.52-MHz
K8-class CPU)
machdep.acpi_timer_freq: 3579545
machdep.tsc_freq: 3790522507
machdep.i8254_freq: 1193182
dev.cpu.0.freq: 349
dev.cpu.0.freq_levels: 2793/130000 2443/113750 2094/97500 1745/81250
1396/65000 1047/48750 698/32500 349/16250
You may be able to use the cpuctl kernel module with sysutils/x86info
to see when the CPUs are using Turbo mode. I haven't had any success
yet but I know in Windows the System control panel reported the 2.66GHz
CPU running at 2.83GHz without me doing anything, so I guess FreeBSD
should be doing the same.
So I managed to test that the Turbo Mode is working. Here is how I
tested it, if it can be useful for other people in the future:
I wrote this very dumb program in C (compiled using gcc -lpthread -o
test test.c):
#include <stdlib.h>
#include <pthread.h>
#include <stdio.h>
int main(int nargs, char* args[]);
void* floop(void* args);
long long int niters;
int main(int nargs, char* args[])
{
int nthrs;
int i;
pthread_t *threads;
--nargs;
++args;
if(nargs!=2) {
fprintf(stderr,"Usage: loop nthreads niters\n");
return 1;
}
sscanf(args[0],"%i",&nthrs);
sscanf(args[1],"%lli",&niters);
printf("Number of threads: %i\n",nthrs);
printf("Number of iterations: %lli\n",niters);
threads=(pthread_t*)malloc(nthrs*sizeof(pthread_t));
for(i=nthrs-1; i>=0; --i) pthread_create(threads+i,NULL,floop,NULL);
for(i=nthrs-1; i>=0; --i) pthread_join(threads[i],NULL);
free(threads);
return 0;
}
void* floop(void* args){
long long int i;
for(i=niters-1; i>=0; --i);
return NULL;
}
I ran it with 8 threads and 150 000 000 000 iterations/threads using
time ./test 8 150000000000
I got a user time of 1827.24 sec with turbo and 1908.69 sec without, a
4.5% speed difference, which is pretty close to the expected 5% (1-21/20
where 21/20 is the ratio of CPU multipliers with and without turbo for
my i7 920 CPU)
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