Re: NTP dumps Linux, film at 11. [Fwd/FYI]

Philip Gladstone (philip@raptor.com)
Tue, 01 Dec 1998 17:22:44 -0500

This is a cryptographically signed message in MIME format.

--------------msBD93012B7E6508A8F5194DC3
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

It turns out that these problems can be mitigated by a patch
like:

--- time.c.orig Fri Oct 2 15:09:15 1998
+++ linux/arch/i386/kernel/time.c Tue Oct 6 14:57:45 1998
@@ -409,9 +409,18 @@
*/
static void pentium_timer_interrupt(int irq, void *dev_id, struct
pt_regs *regs)
{
- register unsigned long edx asm("dx");
+ register unsigned long edx;
int count, flags;

+ int usecs;
+
+ for (usecs = do_fast_gettimeoffset();
+ usecs >= 18000;
+ usecs -= 10000) {
+ /* Try and restore all the dropped interrupts */
+ do_timer(regs);
+ }
+
/* It is important that these two operations happen almost at
the
* same time. We do the RDTSC stuff first, since it's faster.
To
* avoid any inconsistencies, we disable interrupts.

I'm not sure that it will apply to a clean 2.0.36. You also need to
fix do_fast_gettimeoffset not to limit the time returned to be under
one tick (which introduces all sorts of problems anyway).

I run a kernel patch with Ingo Molnar's fix to calibrate the TSC
and then use that value to convert TSC values into usecs.

Philip

Theodore Y. Ts'o wrote:
>
> Date: Mon, 30 Nov 1998 17:48:18 -0500
> From: "Brandon S. Allbery KF8NH" <allbery@kf8nh.apk.net>
>
> What's involved? We use NTP quite a lot, especially for the Linux
> boxes (RH5 systems tend to drift a *lot* for some strange
> reason...
>
> Well, one thing which I recently noticed is that if you're using a
> BusToaster SCSI PCMCIA card (great name, isn't it? :-) It's basically
> Adaptec 152x controller), and you run mke2fs -c on a JAZ drive, your
> clock will slow down an amazing amount --- over five minutes over the
> course of that single command (which was enough to make Kerberos
> complain about clock skew problems).
>
> So there are at least a few device drivers which are apparently holding
> interrupts off long enough so that we lose a clock interrupt. Not good,
> and one of the reasons why any attempts to tweak the Linux scheduler to
> make it a "real-time system" simply elicits a smile from me..... oh, if
> only it were so easy! :-)
>
> - Ted
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.rutgers.edu
> Please read the FAQ at http://www.tux.org/lkml/

-- 
Philip Gladstone                           +1 781 530 2461
Raptor Systems / Axent Technologies 
Waltham, MA                         http://www.raptor.com/
--------------msBD93012B7E6508A8F5194DC3
Content-Type: application/x-pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature

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--------------msBD93012B7E6508A8F5194DC3--




-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/