timer counter chip access mystery]

[Petri Helenius]

I thought you have to use ACPI-safe if you have broken hardware and othervise
you´ll have ACPI-fast. (which my boxes default to)

Pete

----- Original Message ----- 
From: "Jin Guojun [DSD]" <j_guojun at lbl.gov>
To: "Petri Helenius" <pete at he.iki.fi>
Cc: "Steven Hartland" <killing at barrysworld.com>; <freebsd-performance at freebsd.org>
Sent: Thursday, July 17, 2003 2:22 AM
Subject: Re: timer counter chip access mystery]


> 5.1 defaults to use ACPI-safe, which calls read_counter() at least
> three times. The total cost is 3098 ns. So, it meas that read_count()
> cost is about 1000 ns, which is close to what the Linux does.
>
> The rest question is how much error will be if not to use
> ACPI-safe? i.e., sysctl kern.timecounter.hardware=ACPI?
>
>     -Jin
>
> /*
>  * Fetch current time value from reliable hardware.
>  */
> static unsigned
> acpi_timer_get_timecount(struct timecounter *tc)
> {
>     return (read_counter());
> }
>
> /*
>  * Fetch current time value from hardware that may not correctly
>  * latch the counter.
>  */
> static unsigned
> acpi_timer_get_timecount_safe(struct timecounter *tc)
> {
>     unsigned u1, u2, u3;
>
>     u2 = read_counter();
>     u3 = read_counter();
>     do {
>         u1 = u2;
>         u2 = u3;
>         u3 = read_counter();
>     } while (u1 > u2 || u2 > u3 || (u3 - u1) > 15);
>     return (u2);
> }
>
> Petri Helenius wrote:
>
> > 5.x defaults to ACPI or TSC timers. So your wish has been transported
> > by a timemachine into the past.
> >
> > With 4.x you have to set it manually.
> >
> > Pete
> >
> > ----- Original Message -----
> > From: "Steven Hartland" <killing at barrysworld.com>
> > To: "Petri Helenius" <pete at he.iki.fi>; "Jin Guojun [DSD]" <j_guojun at lbl.gov>; <freebsd-performance at freebsd.org>
> > Sent: Thursday, July 17, 2003 12:57 AM
> > Subject: Re: timer counter chip access mystery]
> >
> > > If this could be changed / fixed it would have a marked performance increase
> > > for all game server code which use this function heavily from what I've seen
> > > and would explain the sometimes huge performance differential between
> > > FreeBSD and Linux.
> > >
> > >     Steve / K
> > > ----- Original Message -----
> > > From: "Petri Helenius" <pete at he.iki.fi>
> > > To: "Jin Guojun [DSD]" <j_guojun at lbl.gov>; <freebsd-performance at freebsd.org>
> > > Sent: Wednesday, July 16, 2003 10:44 PM
> > > Subject: Re: timer counter chip access mystery]
> > >
> > >
> > > >
> > > > This access happens over ISA bus and thus happens at the speed the bus
> > > > operates at. Use TSC or ACPI for faster gettimeofday.
> > > >
> > > > Pete
>
>