Date: Sat, 9 Apr 2011 08:29:21 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Jung-uk Kim <jkim@FreeBSD.org> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r220459 - head/sys/x86/isa Message-ID: <20110409075110.L834@besplex.bde.org> In-Reply-To: <201104081954.p38JsTED090284@svn.freebsd.org> References: <201104081954.p38JsTED090284@svn.freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, 8 Apr 2011, Jung-uk Kim wrote:
> Log:
> Refactor DELAYDEBUG as it is only useful for correcting i8254 frequency.
Er, DELAYDEBUG has nothing to do with the i8254 except that the non-i8254
case was broken (mostly in unreachable code, and missing instrumentation
corresponding to the getit_calls counter). Now it is more broken --
e.g., configuring DELAYDEBUG now prevents the non-i8254 timers from
even being compiled.
The core of DELAYDEBUG was essentially just:
for (n1 = 1; n1 <= 10000000; n1 *= 10) {
printf("DELAY(%d)...", n1);
DELAY(n1);
printf("done\n");
}
This could be in an extern function, and works for any implementation of
DELAY(). You observe the resulting delays and fix them if they are too
short or too long (the observation can only be done fairly accurately
for the 2 or 3 final delays of 1/10, 1 and 10 seconds, unless these are
very inaccurate). But it is implemented as a special state in DELAY()
itself, with the printfs separate from the loop, for convenience and
to allow the printfs to print implementation-specific details.
Perhaps the complications for the state are not useful for debugging
the i8254 case now, since the i8254 has a fixed frequency and is well
understood and debugged. The delay_timecounter() case doesn't even
need to be debugged at this level, since if the timecounter is broken
then this will be obvious from userland. But the complications are
useful for the delay_tsc() case, since the TSC doesn't have a fixed
frequency and is often miscalibrated.
Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20110409075110.L834>