Messages in this thread Patch in this message | | | Date | Tue, 01 Dec 1998 17:22:44 -0500 | From | Philip Gladstone <> | Subject | Re: NTP dumps Linux, film at 11. [Fwd/FYI] |
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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/[unhandled content-type:application/x-pkcs7-signature] | |