Date: Sat, 9 Apr 2005 04:48:39 +1000 From: Peter Jeremy <PeterJeremy@optushome.com.au> To: "M. Warner Losh" <imp@bsdimp.com> Cc: freebsd-current@freebsd.org Subject: Re: machdep.conspeed sysctl Message-ID: <20050408184838.GC89047@cirb503493.alcatel.com.au> In-Reply-To: <20050407.211210.100582852.imp@bsdimp.com> References: <200504061737.18204.michaelnottebrock@gmx.net> <20050407.211210.100582852.imp@bsdimp.com>
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On Thu, 2005-Apr-07 21:12:10 -0600, M. Warner Losh wrote:
>In message: <200504061737.18204.michaelnottebrock@gmx.net>
> Michael Nottebrock <michaelnottebrock@gmx.net> writes:
>: However, a loader-tunable comconsole speed would *really* be useful IMHO, so
>: perhaps someone could try and make it happen for real? :-)
>
>I backed it out because there was some problem that bde pointed out to
>me. I can no longer recall what that was...
The log says:
"Until I can figure out how to live without the volatile qualifier on
comdefaultrate, comment out the support for machdep.conspeed for now."
Presumably gcc and/or bde complained that TUNABLE_INT() expected an
"int *" but was passed "volatile int *".
bde made it volatile in 1.162 though it's not clear to me why the
volatile is needed here. I probably need to go and have a close study
of exactly what a compiler is permitted to optimise away in the
absence of 'volatile'.
Rather than try and remove the 'volatile', an alternative approach would
be to expand TUNABLE_INT() and use a an alternative to tunable_int_init()
that could handle the volatile: Replace the current line with (untested):
void
tunable_comdefaultrate_init(void *data __unused)
{
int rate;
TUNABLE_INT_FETCH("machdep.conspeed", &rate);
comdefaultrate = rate;
}
SYSINIT(Tunable_init_comdefaultrate, SI_SUB_TUNABLES, SI_ORDER_MIDDLE, \
tunable_comdefaultrate_init, NULL)
--
Peter Jeremy
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