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Date: Thu, 22 Feb 2007 09:26:52 -0800 (PST) From: David Miller <davem@...emloft.net> To: tglx@...utronix.de Cc: jengelh@...ux01.gwdg.de, kronos.it@...il.com, linux-kernel@...r.kernel.org Subject: Re: NO_HZ: timer interrupt stuck From: Thomas Gleixner <tglx@...utronix.de> Date: Thu, 22 Feb 2007 16:51:41 +0100 > PIT and local APIC timer are used to provide either periodic or one shot > programmable timer events. > > Up to now the kernel started PIT and local APIC timer in parallel with > the same period where PIT incremented jiffies and local APIC timer > called update_process_times() and profile_tick. We changed this to let > the boot cpu increment jiffies inside the local apic timer interrupt > after PIT has been stopped. A whole interrupt for jiffies64++ is waste. BTW, I'm adding support for sparc64, and before I get much further will the code handle a oneshot-only device? That's basically what I have (sparc64 basically has a TSC and a "comparison" register, you write the "comparison" register with the TSC value at which you'd like the timer interrupt to occur, so it's one-shot and you have to write it again to get the next timer). I see logic in the generic code to do periodic events when the timer only provides one-shot ticks. But as far as I can tell both the HPET and the local APIC support periodic timers so I can't tell how much testing that code has gotten :-) I, in fact, don't see any clockevent device in the current tree that does not set CLOCK_EVT_FEAT_PERIODIC. I guess you could clear that bit just to test those generic code paths. :-) BTW, sparc64 always did the trick where the do_timer() work was done by one of the per-cpu local timer interrupts, I'm glad the idea gained traction generically. :-))) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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