Re: git: 8254: Don't setup 8254 interrupt, if it is not selected as interrupt cputimer

[Sepherosa Ziehau <sepherosa@xxxxxxxxx>]

On Sat, Mar 26, 2011 at 2:28 AM, Matthew Dillon
<dillon@apollo.backplane.com> wrote:
>
> :    8254: Don't setup 8254 interrupt, if it is not selected as interrupt cputimer
> :
> :    8254 interrupt is setup, mainly to support C-state > C1, however, on some
> :    systems it could cause system freezing during boot.  Change the default value
> :    of hw.i8254.intr_disable to 1, so more systems could boot by default.
> :
> :Summary of changes:
> : sys/platform/pc32/isa/clock.c |    2 +-
> : sys/platform/pc64/isa/clock.c |    2 +-
> : 2 files changed, 2 insertions(+), 2 deletions(-)
> :
> :http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/4d517764e9560547d731a4d2695a7d8842e33c28
>
>    Hmm.  Are we assuming that HPET or ACPI timers will always be available
>    now?  Any kernel loaded without ACPI won't see the ACPI timer (I think),

No, i8254 is always available as non-interrupt cputimer.  User can't
change that, i.e. no tunable to prevent i8254 to become a usable
non-interrupt cputimer.  It is not changed by this commit, so ACPI is
not a must.

>    and maybe not the HPET either.  The implication is that ACPI must always
>    be loaded now.
>
>    Maybe the real question is... if no other timers are available will the
>    8254 still be used to generate interrupts with this new default?

Yes, if i8254 is selected as interrupt cputimer (normally means lapic
is not available), hw.i8254.intr_disable will be ignored.

Best Regards,
sephe

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