This is a discussion on Re: RFC: PCI SD host controller driver & mmc/mmcsd modulesimprovements - FreeBSD ; Taku YAMAMOTO wrote: > On Thu, 16 Oct 2008 09:28:44 -0600 (MDT) > "M. Warner Losh" wrote: > >> In message: >> Alexander Motin writes: >> : No, it's opposite. With lower frequency I have proportionally smaller >> : delays ...
Taku YAMAMOTO wrote:
> On Thu, 16 Oct 2008 09:28:44 -0600 (MDT)
> "M. Warner Losh"
>> In message: <48F75773.7030100@FreeBSD.org>
>> Alexander Motin
>> : No, it's opposite. With lower frequency I have proportionally smaller
>> : delays (more loop iterations). I don't remember exact numbers now, but
>> : general tendency was like: with 2400MHz - 10 iterations, with 1200MHz -
>> : 20 iterations and with 100MHz - 240 iterations. But neither syslog, nor
>> : my eyes saw any visible delay there.
>> You have more iterations. I'd have expected less. This doesn't say
>> anything at all about DELAY, per se. If you are waiting for 1M cycles
>> at 100MHz, it is only .01s, while at 10MHz it is .1s. Delay is
>> implemented by reading a counter in the 8254 that's been calibrated.
>> So unless the clock that's clocking it is running FASTER, delay won't
>> be the source of additional iterations.
>> Hmmm, looking at the i386 delay code, it looks like it depends on
>> tsc_frequency being right when tsc isn't broken. If that's set
>> bogusly, that could cause DELAY to be slower...
> I have a Core 2 Duo whose TSC ticks regardless of how EST is set.
> In conjunction of tsc_freq_changed() function defined in tsc.c,
> tsc_freq becomes lower than actual, thus shorter DELAY().
> Maybe his machine has the same.
CPU: Intel(R) Core(TM)2 Duo CPU T7700 @ 2.40GHz (2394.01-MHz
Origin = "GenuineIntel" Id = 0x6fb Stepping = 11
Cores per package: 2
FreeBSD 8.0-CURRENT amd64.
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