Messages in this thread | | | Date | Wed, 20 Aug 2003 10:10:47 +0200 | From | Vojtech Pavlik <> | Subject | Re: [PATCH][2.6][5/5]Support for HPET based timer |
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On Tue, Aug 19, 2003 at 06:28:40PM -0700, Pallipadi, Venkatesh wrote: > > I experimented with HPET in native APIC routing mode. But, there > are couple of issues in that space: > > 1) During boot up kernel expects to receive timer interrupt much > before the IO-APIC initialization is done. If HPET uses native mode, > it cannot generate timer interrupts till IOAPICs are initialized. So, > we need to have some sort of Workarounds in generic kernel to avoid > dependency on timer interrupt during the early boot.
Yes, that is a problem. We could do some switchover from PIT to HPET (or from legacy to IOAPIC IRQs) after APICs are initialized, though I don't like the idea very much. Best would be to remove the dependence on the timer interrupt ticking so early. Or moving APIC detection earlier.
> 2) More important question is, do we really want to share timer > interrupt with other PCI devices? This potentially can add some delay > in the timer interrupt processing, and thus we may end up getting > inaccurate time (and inaccurate timer interrupts) in the kernel.
Well, the APIC should have quite a number of free pins, which means that the HPET shouldn't need to share an interrupt. Regarding lost and late delivered timer interrupts - that happens nevertheless with drivers disabling interrupts for a long time. The kernel timekeeping code can cope with that.
> Thanks, -Venkatesh > > -----Original Message----- From: Vojtech Pavlik > > [mailto:vojtech@suse.cz] Sent: Tuesday, August 19, 2003 3:41 PM To: > > Pallipadi, Venkatesh Cc: linux-kernel@vger.kernel.org; > > torvalds@osdl.org; Nakajima, Jun; Mallick, Asit K Subject: Re: > > [PATCH][2.6][5/5]Support for HPET based timer > > > > > > On Tue, Aug 19, 2003 at 12:20:22PM -0700, Pallipadi, Venkatesh > > wrote: > > > > > 5/5 - hpet5.patch - This can be a standalone patch. Without this > > > patch we loose interrupt generation capability of RTC (/dev/rtc), > > > due to HPET. With this patch we basically try to emulate RTC > > > interrupt functions in software using HPET counter 1. > > > > > > > This is very wrong IMO. We shouldn't try to emulate the RTC > > interrupt for the kernel, instead the HPET should use native APIC > > interrupt routing. This way the RTC will keep working and the > > 'legacy mode' of HPET doesn't need to be used. I must admit I was a > > bit lazy when I was implementing the x86_64 variant and the native > > IRQ for HPET is still on my to-do list. > > > > -- Vojtech Pavlik SuSE Labs, SuSE CR > > >
-- Vojtech Pavlik SuSE Labs, SuSE CR - 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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