Messages in this thread | | | Date | Fri, 20 Oct 2006 13:54:50 -0700 | From | Andrew Morton <> | Subject | Re: various laptop nagles - any suggestions? (note: 2.6.19-rc2-mm1 but applies to multiple kernels) |
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On Fri, 20 Oct 2006 22:37:31 +0200 Ingo Molnar <mingo@elte.hu> wrote:
> > * Andrew Morton <akpm@osdl.org> wrote: > > > > > I don't know how many machines will be affected by this, but I'd > > > > expect it's quite a few - the Vaio has a less-than-one-year-old > > > > Intel CPU in it. > > > > > > Is this still the broken lapic issue ? > > > > yup. iirc the standard FC5 SMP kernel runs dog-slowly on that machine > > too. > > hm. This is how lapic timer calibration works. > > the lapic timer is really simple - it counts down from a value and > generates an irq if that counter reaches 0. Then it starts counting down > again. > > the 'count down from' value is programmed via __setup_APIC_LVTT(). > > we first write a 'really large' number into it (1 billion): > > __setup_APIC_LVTT(1000000000); > > the unit of counting is '16 system bus cycles'. > > i.e. if your system has a system bus of 333 MHz, then a value of 1 > billion takes 48 seconds to count down. (so the calibration ought to be > pretty robust in this regard.) > > then we use the wait_timer_tick() function, which waits until the PIT > counter reaches 0 (which is attached to the PIT whose frequency we know > and thus the PIT is already programmed correctly). Hence by calling > wait_timer_tick() we can generate a delay of one jiffy - and we can read > out the current lapic timer count and determine the calibration factor. > > then we calculate the result as: > > result = (tt1-tt2)*APIC_DIVISOR/LOOPS; > > where tt1 is the counter before we start calibration, tt2 is the lapic > timer counter after we did calibration. (APIC_DIVISOR is 16) > > i dont see where the error is - but there must be some calibration > problem as your system shows a systematic 1:60 difference between > expected and real lapic timer frequency. >
Oh. I thought the problem was that the timer stops when the CPU is idle. Maybe I misremembered. I'll try `idle=poll'. - 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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