2009/8/2 Greg KH <greg@xxxxxxxxx>:
> On Sat, Aug 01, 2009 at 03:36:21PM -0400, Robert P. J. Day wrote:
>> On Sat, 1 Aug 2009, Greg KH wrote:
>>
>> > On Fri, Jul 31, 2009 at 11:23:15AM +0700, Mulyadi Santosa wrote:
>> > > On Fri, Jul 31, 2009 at 6:52 AM, Karel Zak<kzak@xxxxxxxxxx> wrote:
>> > > It seems that user space sees HZ as 100, while in fact my current
>> > > running kernel is compiled with HZ=300. What do you think about it? Or
>> > > is there something wrong with my conclusion?
>> >
>> > The following C program should properly show you the kernel HZ.
>> >
>> > thanks,
>> >
>> > greg k-h
>> >
>> > --------------
>> >
>> > #include <unistd.h>
>> > #include <time.h>
>> > #include <stdio.h>
>> >
>> > int main()
>> > {
>> > struct timespec res;
>> > double resolution;
>> >
>> > printf("UserHZ %ld\n", sysconf(_SC_CLK_TCK));
>> >
>> > clock_getres(CLOCK_REALTIME, &res);
>> > resolution = res.tv_sec + (((double)res.tv_nsec)/1.0e9);
>> >
>> > printf("SystemHZ %ld\n", (unsigned long)(1/resolution + 0.5));
>> > return 0;
>> > }
>>
>> i already knew about sysconf. so i'm going to assume there's no
>> simpler way to get the current HZ (either command line or /proc
>> based).
>
> But the point is, from userspace's point of view, the kernel HZ value
> means NOTHING. See the above program that shows what the resolution
> that userspace can use is. That is what userspace cares about, and what
> the kernel provides. Internal HZ values of what the kernel might use
> for scheduling means _nothing_.
>
but some applications or drivers especially for stream media i think
they need this parameter to get a balance for performance.
refer to the link: http://lwn.net/Articles/145973/
i think people need it to configure their kernel.
> So if you do provide it to userspace in a proc file, what then? What is
> userspace going to do with such a value? It should never depend on it,
> because it doesn't matter to it.
>
how do we change the kernel HZ parameter except reconfiguration kernel
and rebuild kernel?
Nowadays with the big kernel, rebuild it again and again i think it is
not a very happy thing.
Do the kernel have a mechanism to change all the configuration
dynamically without rebuilding kernel?
BRs
Lin
> thanks,
>
> greg k-h
>
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