6 Commits

Author SHA1 Message Date
marius
5f0e19e7df Use the STICK timers only when absolutely necessary, i.e. if a machine
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
2008-09-20 11:26:13 +00:00
marius
a030d21a6f - USIII-based machines can consist of CPUs running at different
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.
2008-09-03 17:39:19 +00:00
marius
fe74973b39 - Add a workaround for a bug in BlackBird CPUs (said to be part of the
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]
2005-04-16 14:57:38 +00:00
tmm
f2106ce588 Initialize tick_MHz and related variables much earlier. After the last
revision of tick.c, this was done at SI_SUB_CLOCKS, which is too late
because tick_MHz is required for DELAY() to work.

Reviewed by:	jake
2002-10-25 17:42:14 +00:00
jake
2b8f2f82cf Add support for driving the clocks on secondary cpus.
Submitted by:	tmm
2002-03-13 04:38:33 +00:00
jake
cdce7694e2 Add code to program the tick register and to setup its interrupt handler. 2001-08-10 04:49:33 +00:00