a critical section as apparently required by both. I don't think either
belongs in the event timer front-ends but the callback should handle
this as necessary instead just like for example intr_event_handle()
does but this is how the other architectures currently handle it, either
explicitly or implicitly.
- Further rename and reword references to hardclock as this front-end no
longer has a notion of actually calling it.
but also of different types, f.e. Sun Fire V890 can be equipped with a
mix of UltraSPARC IV and IV+ CPUs, requiring different MMU initialization
and different workarounds for model specific errata. Therefore move the
CPU implementation number from a global variable to the per-CPU data.
Functions which are called before the latter is available are passed the
implementation number as a parameter now.
This file was missed in r204152.
consists of CPUs running at different speeds, for driving hardclock as
these timers in turn are driven at frequencies as low as 5MHz, resulting
in bad granularity compared to the TICK timers. However, don't employ
the workaround for the BlackBird erratum #1 when using the TICK timer
on machines with cheetah-class CPUs for performance reasons.
Reported by: Florian Smeets
frequencies (and having different cache sizes) so use the STICK
(System TICK) timer, which was introduced due to this and is
driven by the same frequency across all CPUs, instead of the
TICK timer, whose frequency varies with the CPU clock, to drive
hardclock. We try to use the STICK counter with all CPUs that are
USIII or beyond, even when not necessary due to identical CPUs,
as we can can also avoid the workaround for the BlackBird erratum
#1 there. Unfortunately, using the STICK counter currently causes
a hang with USIIIi MP machines for reasons unknown, so we still
use the TICK timer there (which is okay as they can only consist
of identical CPUs).
- Given that we only (try to) synchronize the (S)TICK timers of APs
with the BSP during startup, we could end up spinning forever in
DELAY(9) if that function is migrated to another CPU while we're
spinning due to clock drift afterwards, so pin to the CPU in order
to avoid migration. Unfortunately, pinning doesn't work at the
point DELAY(9) is required by the low-level console drivers, yet,
so switch to a function pointer, which is updated accordingly, for
implementing DELAY(9). For USIII and beyond, this would also allow
to easily use the STICK counter instead of the TICK one here,
there's no benefit in doing so however.
While at it, use cpu_spinwait(9) for spinning in the delay-
functions. This currently is a NOP though.
- Don't set the TICK timer of the BSP to 0 during at startup as
there's no need to do so.
- Implement cpu_est_clockrate().
- Unfortunately, USIIIi-based machines don't provide a timecounter
device besides the STICK and TICK counters (well, in theory the
Tomatillo bridges have a performance counter that can be (ab)used
as timecounter by configuring it to count bus cycles, though unlike
the performance counter of Schizo bridges, the Tomatillo one is
broken and counts Sun knows what in this mode). This means that
we've to use a (S)TICK counter for timecounting, which has the old
problem of not being in sync across CPUs, so provide an additional
timecounter function which binds itself to the BSP but has an
adequate low priority.
SpitFire erratum #54) which can cause writes to the TICK_CMPR register
to fail. This seems to fix the dying clocks problem reported by jhb@
and kris@. [1]
- In tick_start() don't reset the tick counter of the boot processor to
zero. It's initially reset in _start() and afterwards but _before_
tick_start() is called on the BSP the APs synchronise with the tick
counter of the BSP in mp_startup(). Resetting the tick counter of the
BSP in tick_start() probably also was the cause of problems seen when
using the CPU tick counter as timecounter on SMP machines.
Not resetting the tick counter of the BSP in mp_startup() makes the
tick counters and tick interrupts between the BSP and APs be pretty
much in sync as it's supposed to be. This also means there's no longer
a real reason to have separate tick_start() and tick_start_ap() so
merge them and zap tick_start_ap(). This is also a first step in
simplifying the interface to the tick counters in preparation to use
alternate clock hardware where available.
- Switch to the algorithm used on FreeBSD/ia64 for updating the tick
interrupt register and which compensates the clock drift caused by
varying delays between when the tick interrupts actually trigger and
when they are serviced. Not compensating the clock drift mainly hurts
interactive performance especially when using WITNESS. [2]
For further information about the algorithm also see the commit log
of sys/ia64/ia64/interrupt.c rev. 1.38.
On sparc64 the sysctls for monitoring the behaviour of the tick
interrupts are machdep.tick.adjust_edges, machdep.tick.adjust_excess,
machdep.tick.adjust_missed and machdep.tick.adjust_ticks.
- In tick_init() just use tick_stop() for stopping the tick interrupts
until a proper handler is set up later. This also stops the system
tick interrupt on USIII systems earlier.
- In tick_start() check for a rough upper limit of HZ.
- Some minor changes, e.g. use FBSDID, remove unused headers, etc.
Info obtained from: Linux [1]
Ok'ed by: marcel [2]
Additional testing by: kris (earlier version of the workaround), jhb
X-MFC after: 3 days [1]
