Messages in this thread | | | Date | Thu, 14 Nov 2002 00:08:51 -0800 | From | george anzinger <> | Subject | Re: local APIC may cause XFree86 hang |
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Linus Torvalds wrote: > > On Wed, 13 Nov 2002, Nakajima, Jun wrote: > > > > The one instance I saw was that the BIOS was reading 8254 in a tight loop > > for a calibration purpose, and it was assuming the time proceeded in a > > constant speed, to exit the loop. In other words, it never assumed it could > > get interrupts. To vm86, interrupts are invisible, but they have impacts on > > the actual speed. > > That sound slike a perfectly ok thing to do - apart from the hw latching > which might confuse the kernel.
Yes, it has been speculated that some "time warps" were caused by "someone" reading only one of the two bytes from the PIT. It puts the following reads out of sync. If this was caused by an interrupt (which, of course, is where the PIT is read by the kernel) between two reads, it could well cause the "time warps" that have been observed.
George > > When enabling the local APIC, Linux doesn't actually disable legacy PIT > interrupts, so again I don't really see what the apparent connection > between the hang and the APIC is. So I'd still suspect it's more > timing-related than anything else. > > Linus > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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