Date: Wed, 21 Jul 2010 20:22:36 -0700 From: Neel Natu <neelnatu@gmail.com> To: Alexander Motin <mav@freebsd.org> Cc: freebsd-mips@freebsd.org Subject: Re: [RFC] Event timers on MIPS Message-ID: <AANLkTinrTzPZF0NbnT2e8kf8E4KtCwXUfFH7i1nBP_kz@mail.gmail.com> In-Reply-To: <4C4698D6.2090104@FreeBSD.org> References: <4C41A248.8090605@FreeBSD.org> <4C4698D6.2090104@FreeBSD.org>
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Hi Alexander,
Your patch works fine on a Sibyte. I verified that wall clock time is
progressing as expected. Is there any other test that you recommend?
I have a few comments about the patch:
1. set_cputicker() in clock_attach() should be moved back up to
mips_timer_init_params(). Otherwise the platform-specific CPU tickers
used by Sibyte, Octeon and RMI will be overwritten by the mips32 ticker.
2. The local variable 'cycles_per_tick' in clock_intr() can now be a uint32_t.
3. Is there a race between setting 'cycles_per_tick' in clock_start() and
clock_intr()? Would it be better to write the compare register first
and then set 'cycles_per_tick' to a non-zero value?
If I understand the code correctly we are liable to get clock interrupts
even afer the clock is stopped when the CP0 COUNT register matches
0xffffffff.
4. We need to update the DPCPU(compare_ticks) value when we start the timer
in clock_start().
5. I think the entire 'lost_ticks' processing in clock_intr() should be
conditional on (cycles_per_tick > 0). Without this we may incorrectly
update the value of DPCPU(lost_ticks).
6. Can you a couple of lines of explaining the computatation of
'et_min_period' and 'et_max_period'? It is not completely obvious to me.
best
Neel
2010/7/20 Alexander Motin <mav@freebsd.org>:
> Alexander Motin wrote:
>> I've made a patch, updating MIPS timer code (except RMI) to utilize new
>> MI event timer infrastructure. I've successfully built QEMU and XLR
>> kernels with the patch. Unluckily I can't test how it works, unless
>> somebody teach me how to cook QEMU to run it. I also haven't ported RMI
>> timers drivers, as I am not sure how that hardware is intended to work.
>>
>> Patch for HEAD can be found here:
>> http://people.freebsd.org/~mav/timers_mips.patch
>
> Slightly updated version for fresh HEAD:
> http://people.freebsd.org/~mav/timers_mips2.patch
>
> --
> Alexander Motin
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