Date: Sat, 02 Jun 2007 17:30:10 -0700 From: Nate Lawson <nate@root.org> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: takawata@freeBSD.org, Dag-Erling Sm??rgrav <des@des.no>, current@freeBSD.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: HPET vs other timers Message-ID: <46620B92.8020608@root.org> In-Reply-To: <47223.1180818913@critter.freebsd.dk> References: <47223.1180818913@critter.freebsd.dk>
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Poul-Henning Kamp wrote:
> Nate Lawson wrote:
>>> Anyone able to speculate why though? HPET only reads 32 bits from a
>>> memory mapped region. No locking or other requirements. ACPI_timer
>>> does multiple IO ops, which according to bde@ are much slower than
>>> memory reads.
>
> HPET needs to do metastability mitigation and is not "just a read
> from a memory mapped region".
If it does, then it's not implemented yet:
static u_int
hpet_get_timecount(struct timecounter *tc)
{
struct acpi_hpet_softc *sc;
sc = tc->tc_priv;
return (bus_read_4(sc->mem_res, HPET_OFFSET_VALUE));
}
Are you sure you're not thinking of ACPI-safe?
--
Nate
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