Date: Wed, 16 Jul 2003 16:22:58 -0700 From: "Jin Guojun [DSD]" <j_guojun@lbl.gov> To: Petri Helenius <pete@he.iki.fi> Cc: Steven Hartland <killing@barrysworld.com> Subject: Re: timer counter chip access mystery] Message-ID: <3F15DE52.130D8FA9@lbl.gov> References: <3F15C584.38848DCE@lbl.gov> <071401c34be3$71a03510$812a40c1@PETEX31> <00b501c34be5$351a83f0$b3db87d4@vader> <075101c34be5$db5e4c10$812a40c1@PETEX31>
next in thread | previous in thread | raw e-mail | index | archive | help
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@barrysworld.com>
> To: "Petri Helenius" <pete@he.iki.fi>; "Jin Guojun [DSD]" <j_guojun@lbl.gov>; <freebsd-performance@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@he.iki.fi>
> > To: "Jin Guojun [DSD]" <j_guojun@lbl.gov>; <freebsd-performance@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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3F15DE52.130D8FA9>