On Fri, May 08, 2009 at 11:45:16AM +1000, Bruce Evans wrote: > On Thu, 7 May 2009, Dmitry Chagin wrote: > > > Log: > > Linux exports HZ value to user space via AT_CLKTCK auxiliary vector entry, > > which is available for Glibc as sysconf(_SC_CLK_TCK). If AT_CLKTCK entry is > > not exported, Glibc uses 100. > > This cannot work for older applications/glibc's that have CLK_TCK hard-coded. >
yes, I know. Glibc versions prior to 2.2.1 uses hardcoded CLK_TCK value.
> > linux_times() shall use the value that is exported to user space.
>
> FreeBSD handles the problem by "exporting" the old constant value of CLK_TCK
> (128) although this value has always been bogus and the "export" is actually
> hard-coded into libc:sysconf() (and into <time.h> except in post-2001
> pure-POSIX case -- in particular, the bogus macro CLK_TCK is still hard-
> coded to the bogus value 128 in the BSD_VISIBLE case to avoid breaking
> bogus BSD applications that use it).
>
> > Modified: head/sys/compat/linux/linux_misc.c
> > ==============================================================================
> > --- head/sys/compat/linux/linux_misc.c Thu May 7 13:49:48 2009
> > (r191882)
> > +++ head/sys/compat/linux/linux_misc.c Thu May 7 14:24:50 2009
> > (r191883)
> > @@ -659,9 +659,7 @@ struct l_times_argv {
> > l_clock_t tms_cstime;
> > };
> >
> > -#define CLK_TCK 100 /* Linux uses 100 */
> > -
> > -#define CONVTCK(r) (r.tv_sec * CLK_TCK + r.tv_usec / (1000000 / CLK_TCK))
> > +#define CONVTCK(r) (r.tv_sec * hz + r.tv_usec / (1000000 / hz))
>
> hz has very little to do with statistics clock ticks. The frequency of the
> statistics clock in FreeBSD is given by stathz. stathz will normally only
> equal hz if the statistics clock is the same as the scheduling clock.
> stathz is a bogus value too since the clock most relevant for them is the
> cputicker and the statistics clock is only used to divide them up.
>
Thank you!
> Anyway, this patch is backwards. The bug was that the value exported to
> user space didn't match the value here. The value cannot be changed in
hmm, r189362. hz exported to user space via AT_CLKTCK.
> either FreeBSD or Linux without breaking compatibility. It is even
> harder to change in emulators than in a full O/S distribution since the
> full distribution can more reasonably drop support for all old
> applications. A correct emulator would have to have an array of values
> for each "constant" sysconf() value with the arrays index by the O/S
> version and maybe the libc version being emulated :-(.
>
I will try to make the hard-coded CLK_TCK support. It will depend
on value of compat.linux.osrelease (2.2 I guess).
--
Have fun!
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