[PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[David Engraf]

This patch adds a new systemcall on i386 architectures returning the jiffies
value to the application. 
As a kernel developer you can use jiffies but from the user space there is
no equivalent function which counts every millisecond like the Win32
GetTickCount.

linux-2.6.15-rc5-mm1



diff -puN include/asm-i386/unistd_orig.h include/asm-i386/unistd.h
--- include/asm-i386/unistd_orig.h	2005-12-06 12:07:16.000000000 +0100
+++ include/asm-i386/unistd.h	2005-12-06 12:10:07.000000000 +0100
@@ -300,8 +300,9 @@
 #define __NR_inotify_add_watch	292
 #define __NR_inotify_rm_watch	293
 #define __NR_migrate_pages	294
+#define __NR_tickcount	295
 
-#define NR_syscalls 295
+#define NR_syscalls 296
 
 /*
  * user-visible error numbers are in the range -1 - -128: see




diff -puN arch/i386/kernel/syscall_table_orig.S
arch/i386/kernel/syscall_table.S
--- arch/i386/kernel/syscall_table_orig.S	2005-12-06
12:07:14.000000000 +0100
+++ arch/i386/kernel/syscall_table.S	2005-12-06 12:10:40.000000000 +0100
@@ -294,3 +294,4 @@ ENTRY(sys_call_table)
 	.long sys_inotify_add_watch
 	.long sys_inotify_rm_watch
 	.long sys_migrate_pages
+	.long sys_tickcount



diff -puN kernel/sys_orig.c kernel/sys.c
--- kernel/sys_orig.c	2005-12-06 12:06:49.000000000 +0100
+++ kernel/sys.c	2005-12-06 12:08:57.000000000 +0100
@@ -1855,3 +1855,9 @@ asmlinkage long sys_prctl(int option, un
 	}
 	return error;
 }
+
+asmlinkage long sys_tickcount(long __user *ret)
+{
+	if (copy_to_user(ret, (void*)&jiffies, sizeof(long)))
+	return 0;
+}



Thanks
David Engraf


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Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Arjan van de Ven]

On Tue, 2005-12-06 at 11:36 +0100, David Engraf wrote:
> This patch adds a new systemcall on i386 architectures returning the jiffies
> value to the application. 
> As a kernel developer you can use jiffies but from the user space there is
> no equivalent function which counts every millisecond like the Win32
> GetTickCount.

a few comments

1) jiffies are 64 bit not 32
2) jiffies are not a constant time, eg HZ is a config option,
   exposing that internal counter to userspace sounds wrong, after
   all what would it be used for
3) wouldn't it be better to expose a wallclock time thing which
   has a constant unit of time between all kernels?

(and.. wait.. isn't that called gettimeofday() )

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[David Engraf]

> On Tue, 2005-12-06 at 11:36 +0100, David Engraf wrote:
> > This patch adds a new systemcall on i386 architectures returning the
jiffies
> > value to the application. 
> > As a kernel developer you can use jiffies but from the user space there
is
> > no equivalent function which counts every millisecond like the Win32
> > GetTickCount.

> a few comments

> 1) jiffies are 64 bit not 32

Jiffies is defined as "unsigned long volatile __jiffy_data jiffies". On i386
machines unsigned long is 32.


> 2) jiffies are not a constant time, eg HZ is a config option,
>    exposing that internal counter to userspace sounds wrong, after
>    all what would it be used for

Right, HZ is defined as USER_HZ which can be set over the config. On normal
desktop systems it should be 1000 on other machines it could also be 100 or
250. Either we can ignore the setting and the function depends on the
USER_HZ config, or we have to calculate the right value with USER_HZ. 


> 3) wouldn't it be better to expose a wallclock time thing which
>    has a constant unit of time between all kernels?

What is it?


> (and.. wait.. isn't that called gettimeofday() )
Not really gettimeofday is based on the date and time, but what if the user
changes the date, the counter would also change.



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Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Ingo Molnar]

* David Engraf <engraf.david@netcom-sicherheitstechnik.de> wrote:

> > (and.. wait.. isn't that called gettimeofday() )
>
> Not really gettimeofday is based on the date and time, but what if the 
> user changes the date, the counter would also change.

see 'man clock_gettime', and CLOCK_MONOTONIC:

       CLOCK_MONOTONIC
              Clock that cannot be set and  represents  monotonic  time  since
              some unspecified starting point.

and it has microsecond resolution.

	Ingo

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[David Engraf]

> * David Engraf <engraf.david@netcom-sicherheitstechnik.de> wrote:
> 
> > > (and.. wait.. isn't that called gettimeofday() )
> >
> > Not really gettimeofday is based on the date and time, but what if the
> > user changes the date, the counter would also change.
> 
> see 'man clock_gettime', and CLOCK_MONOTONIC:
> 
>        CLOCK_MONOTONIC
>               Clock that cannot be set and  represents  monotonic  time
> since
>               some unspecified starting point.
> 
> and it has microsecond resolution.
> 
> 	Ingo

You're right, clock_gettime with CLOCK_MONOTONIC seems to be date/time
independent. For a GetTickCount implementation it is absolutely enough.

Thanks
David Engraf


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Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Arjan van de Ven]

On Tue, 2005-12-06 at 12:23 +0100, David Engraf wrote:
> > On Tue, 2005-12-06 at 11:36 +0100, David Engraf wrote:
> > > This patch adds a new systemcall on i386 architectures returning the
> jiffies
> > > value to the application. 
> > > As a kernel developer you can use jiffies but from the user space there
> is
> > > no equivalent function which counts every millisecond like the Win32
> > > GetTickCount.
> 
> > a few comments
> 
> > 1) jiffies are 64 bit not 32
> 
> Jiffies is defined as "unsigned long volatile __jiffy_data jiffies". On i386
> machines unsigned long is 32.

but it's a subvariable of jiffies64 which is 64 bit
> 
> 
> > 2) jiffies are not a constant time, eg HZ is a config option,
> >    exposing that internal counter to userspace sounds wrong, after
> >    all what would it be used for
> 
> Right, HZ is defined as USER_HZ which can be set over the config. On normal
> desktop systems it should be 1000 on other machines it could also be 100 or
> 250. Either we can ignore the setting and the function depends on the
> USER_HZ config, or we have to calculate the right value with USER_HZ. 

but then.. why?

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Jakub Jelinek]

On Tue, Dec 06, 2005 at 12:23:23PM +0100, David Engraf wrote:
> > (and.. wait.. isn't that called gettimeofday() )
> Not really gettimeofday is based on the date and time, but what if the user
> changes the date, the counter would also change.

If you want a monotonic clock, just use clock_gettime (CLOCK_MONOTONIC, &ts);

	Jakub

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Bernd Petrovitsch]

On Tue, 2005-12-06 at 12:23 +0100, David Engraf wrote:
> > On Tue, 2005-12-06 at 11:36 +0100, David Engraf wrote:
[.../9
> > 3) wouldn't it be better to expose a wallclock time thing which
> >    has a constant unit of time between all kernels?
> 
> What is it?
> 
> 
> > (and.. wait.. isn't that called gettimeofday() )
> Not really gettimeofday is based on the date and time, but what if the user
> changes the date, the counter would also change.

man 2 times
And use the returned value.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[David Engraf]

> On Tue, 2005-12-06 at 12:23 +0100, David Engraf wrote:
> > > On Tue, 2005-12-06 at 11:36 +0100, David Engraf wrote:
> [.../9
> > > 3) wouldn't it be better to expose a wallclock time thing which
> > >    has a constant unit of time between all kernels?
> >
> > What is it?
> >
> >
> > > (and.. wait.. isn't that called gettimeofday() )
> > Not really gettimeofday is based on the date and time, but what if the
> user
> > changes the date, the counter would also change.
> 
> man 2 times
> And use the returned value.
> 
> 	Bernd
> --
> Firmix Software GmbH                   http://www.firmix.at/
> mobil: +43 664 4416156                 fax: +43 1 7890849-55
>           Embedded Linux Development and Services

times has only 10ms resolution, we need at least 1ms.

David


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Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Andi Kleen]

"David Engraf" <engraf.david@netcom-sicherheitstechnik.de> writes:
> 
> times has only 10ms resolution, we need at least 1ms.

It actually has jiffies resultion. Your measurements must have been
quite off.

-Andi

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Eric Dumazet]

Andi Kleen a écrit :
> "David Engraf" <engraf.david@netcom-sicherheitstechnik.de> writes:
> 
>>times has only 10ms resolution, we need at least 1ms.
> 
> 
> It actually has jiffies resultion. Your measurements must have been
> quite off.

I beg to differ: times has a 10 ms resolution ( ie 1/USER_HZ)

times() is supposed to return clock_t expressed in USER_HZ, wich is still 100, 
regardless of the kernel HZ

I just checked sources and sys_times() do use jiffies_64_to_clock_t()

Eric

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Andi Kleen]

On Tue, Dec 06, 2005 at 07:00:34PM +0100, Eric Dumazet wrote:
> Andi Kleen a ?crit :
> >"David Engraf" <engraf.david@netcom-sicherheitstechnik.de> writes:
> >
> >>times has only 10ms resolution, we need at least 1ms.
> >
> >
> >It actually has jiffies resultion. Your measurements must have been
> >quite off.
> 
> I beg to differ: times has a 10 ms resolution ( ie 1/USER_HZ)

You're right. Sorry for the confusion. clock_gettime is the way
to go.

-Andi

Re: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[Andi Kleen]

"David Engraf" <engraf.david@netcom-sicherheitstechnik.de> writes:

> This patch adds a new systemcall on i386 architectures returning the jiffies
> value to the application. 
> As a kernel developer you can use jiffies but from the user space there is
> no equivalent function which counts every millisecond like the Win32
> GetTickCount.

You want a timer that never go backwards, right? 

Use clock_gettime(CLOCK_MONOTONIC). It's the POSIX way to do this.

-Andi

AW: [PATCH] Win32 equivalent to GetTickCount systemcall (i386)

[David Engraf]

> "David Engraf" <engraf.david@netcom-sicherheitstechnik.de> writes:
> 
> > This patch adds a new systemcall on i386 architectures returning the
> jiffies
> > value to the application.
> > As a kernel developer you can use jiffies but from the user space there
> is
> > no equivalent function which counts every millisecond like the Win32
> > GetTickCount.
> 
> You want a timer that never go backwards, right?
> 
> Use clock_gettime(CLOCK_MONOTONIC). It's the POSIX way to do this.
> 
> -Andi

Yes, clock_gettime works(CLOCK_MONOTONIC), thanks.

David


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