Date: Fri, 11 Sep 2009 11:05:57 -0400 From: Pierre-Luc Drouin <pldrouin@pldrouin.net> To: freebsd-stable@freebsd.org Subject: Re: How to enable CPU turbo mode on FreeBSD? Message-ID: <4AAA6755.7070502@pldrouin.net> In-Reply-To: <20090911074123.00006179@unknown> References: <4AA9A07C.4050200@pldrouin.net> <20090911074123.00006179@unknown>
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Bruce Cran wrote:
> On Thu, 10 Sep 2009 20:57:32 -0400
> Pierre-Luc Drouin <pldrouin@pldrouin.net> 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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