Messages in this thread | | | Date | Wed, 16 Jun 2004 16:28:26 -0300 | From | Peter Cordes <> | Subject | x86-64: double timer interrupts in recent 2.4.x |
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Nobody replied to this message on debian-amd64@lists.d.o, or discuss@x86-64.org. Hopefully I've found the right places to send this this time around. Actually, Roland Fehrenbacher saw my message in a list archive and mailed me to confirm that he saw the same double-speed clock problem on two different machines, so it's not just Tyan S2880 boards. He suggested I mail Andi and lkml, so here goes. (I haven't tested again with anything more recent than 2.4.27-pre2, so if this is fixed, sorry.)
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I just noticed that on my Opteron cluster, the nodes that are running 64bit kernels have their clocks ticking at double speed. This happens with Linux 2.4.26, and 2.4.27-pre2, compiled with gcc 3.3.3 (Debian 20040401) in a Debian pure64 chroot. Linux 2.4.25, compiled on Debian Woody + bi-arch gcc 3.3.2 20030908, does _not_ have the problem. The config options were pretty much the same for all kernels, and all the kernels are plain vanilla flavour from www.ca.kernel.org.
If I run ntpdate to set the clock, then 10 seconds later it will be 10 seconds fast. Running date(1), the system time advances 20 seconds in 10 seconds of real time. (I haven't done anything weird with adjtimex(8).) time sleep 10 takes 5 seconds, but bash reports its real time as 10 seconds. The timer interrupt counter is increasing at a rate of 200/real second, so it seems like the system is getting timer interrupts twice as fast as it should. (With 2.4.25, it is 100/sec, same as HZ).
Linux says it is using the PIT and TSC timers. I have HPET enabled in my Linux config, but I guess Tyan's S2880 mobo doesn't have one. This is a dual-Opteron 240 machine, BTW.
i386 Linux on the same machines has no problems with timekeeping. (But I haven't tested versions later than 2.4.25 in legacy mode.)
I spent some time poking around the timer code that increments xtime, but I guess the fact that the timer irqs are coming at double speed indicates that the problem lies elsewhere. Maybe the code that sets up the timer?
$ uname -a Linux node6.cs.dal.ca 2.4.26 #2 SMP Fri May 14 14:46:42 ADT 2004 x86_64 x86_64 x86_64 GNU/Linux $ cat /proc/interrupts CPU0 CPU1 0: 4415908 0 IO-APIC-edge timer 1: 2 0 IO-APIC-edge keyboard 2: 0 0 XT-PIC cascade 9: 0 0 IO-APIC-level acpi 14: 17861 1 IO-APIC-edge ide0 19: 0 0 IO-APIC-level usb-ohci, usb-ohci 24: 563942 0 IO-APIC-level eth0 25: 564331 0 IO-APIC-level eth1 NMI: 19097 19097 LOC: 2211090 2211095 ERR: 0 MIS: 0
Only CPU0 is getting the timer interrupt, but at least we know it's not that both CPUs are getting the timer interrupt. (Both CPUs get 100 LOC: (local APIC) interrupts/sec, but that happens on the non-buggy 2.4.25, too.)
Thanks for any help, I'm not subscribed to the lkml, so please CC me on any followups.
-- #define X(x,y) x##y Peter Cordes ; e-mail: X(peter@cor , des.ca)
"The gods confound the man who first found out how to distinguish the hours! Confound him, too, who in this place set up a sundial, to cut and hack my day so wretchedly into small pieces!" -- Plautus, 200 BC [unhandled content-type:application/pgp-signature]
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