Date: Sun, 10 May 2009 00:45:59 +0400 From: Chagin Dmitry <dchagin@freebsd.org> To: Bruce Evans <brde@optusnet.com.au> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r191883 - head/sys/compat/linux Message-ID: <20090509204559.GA4626@dchagin.static.corbina.ru> In-Reply-To: <20090508111302.C1275@besplex.bde.org> References: <200905071424.n47EOos1058369@svn.freebsd.org> <20090508111302.C1275@besplex.bde.org>
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On Fri, May 08, 2009 at 11:45:16AM +1000, Bruce Evans wrote:
> On Thu, 7 May 2009, Dmitry Chagin wrote:
>=20
> > Log:
> > Linux exports HZ value to user space via AT_CLKTCK auxiliary vector en=
try,
> > which is available for Glibc as sysconf(_SC_CLK_TCK). If AT_CLKTCK ent=
ry is
> > not exported, Glibc uses 100.
>=20
> This cannot work for older applications/glibc's that have CLK_TCK hard-co=
ded.
>=20
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.
>=20
> 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 actua=
lly
> 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).
>=20
> > Modified: head/sys/compat/linux/linux_misc.c
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> > --- head/sys/compat/linux/linux_misc.c Thu May 7 13:49:48 2009 (r19188=
2)
> > +++ head/sys/compat/linux/linux_misc.c Thu May 7 14:24:50 2009 (r19188=
3)
> > @@ -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_TC=
K))
> > +#define CONVTCK(r) (r.tv_sec * hz + r.tv_usec / (1000000 / hz))
>=20
> hz has very little to do with statistics clock ticks. The frequency of t=
he
> 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.
>=20
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 :-(.
>=20
I will try to make the hard-coded CLK_TCK support. It will depend
on value of compat.linux.osrelease (2.2 I guess).
--=20
Have fun!
chd
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