This is a discussion on Re: RFC: PCI SD host controller driver & mmc/mmcsd modulesimprovements - FreeBSD ; In message: Taku YAMAMOTO writes: : 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 ...
In message: <email@example.com>
: 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.
That would cause the problem. If we're bogusly adjusting tsc_freq we
should fix that...
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