[RFC v5 00/23] adapt clockevents frequencies to mono clock

[Nicolai Stange <nicstange@gmail.com>]

Goal: avoid programming ced devices too early for large deltas, for
      details, for details, c.f. the description of [21/23].


Previous v4 of this series can be found here:

  http://lkml.kernel.org/r/20160822233320.4548-1-nicstange@gmail.com

Raised concerns were
1.) There should be a flag available which when enabled, should
    exclude a ced from getting its ->mult adjusted.
2.) The ns2cyc multiplication in clockevents_program_event() can
    overflow with the adjusted ->mult.

The first item is addressed by the new
[13/23] ("clockevents: introduce CLOCK_EVT_FEAT_NO_ADJUST flag"),
the second by
[14/23] ("clockevents: decouple ->max_delta_ns from ->max_delta_ticks")

A note regarding the CLOCK_EVT_FEAT_NO_ADJUST flag: we probably want
to set it for the ->mult = 1, ->shift = 0 devices. However, since the
frequency adjustments are small (and bounded), they actually translate
to noops for those ceds. Thus, setting it there would be a matter of
style and optimization and I left this out for now.


This series can be divided into logical subseries as follows:
[1-6/23]   Don't modify ced rate after registrations through mechanisms
           other than clockevents_update_freq().

[7-12/23]  Let all ced devices set their ->*_delta_ticks values and let
           the clockevent core do the rest.

[13/23]    Introduce the CLOCK_EVT_FEAT_NO_ADJUST flag

[14-20/23] Fiddle around with the bound checking code in order to
           allow for non-atomic frequency updates from a CPU different
           than where the ced is programmed.

[21-23/23] Actually do the frequency adjustments.


Tested on x86_64 and next-20160825.


Changes to v4:
 [1-12/23] Unchanged

 [13/23] ("clockevents: introduce CLOCK_EVT_FEAT_NO_ADJUST flag")
   New.

 [14/23] ("clockevents: decouple ->max_delta_ns from ->max_delta_ticks")
   New. Solves the overflow problem the former
   [13/22] ("clockevents: check a programmed delta's bounds in terms of cycles")
   from v4 introduced.

   (Note that the former
    [14/22] ("clockevents: clockevents_program_event(): turn clc into unsigned long")
    from v4 has been purged.)

 [15/23] ("clockevents: do comparison of delta against minimum in terms of cycles")
   This is the former
   [13/22] ("clockevents: check a programmed delta's bounds in terms of cycles"),
   but only for the ->min_delta_* -- the ->max_delta_* are handled by [14/23] now.

 [16/23] ("clockevents: clockevents_program_min_delta(): don't set ->next_event")
   Former [15/22] unchanged.

 [17/23] ("clockevents: use ->min_delta_ticks_adjusted to program minimum delta")
   Former [16/22]. Trivially fix compilation error with
   CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST=n.

 [18/22] ("clockevents: min delta increment: calculate min_delta_ns from ticks")
   Former [17/22] unchanged.

 [19/23] ("timer_list: print_tickdevice(): calculate ->min_delta_ns dynamically")
   Corresponds to former
   [18/22] ("timer_list: print_tickdevice(): calculate ->*_delta_ns dynamically")
   from v4, but only for ->min_delta_ns. The changes required for the display of
   ->max_delta_ns are now being made in [14/23] already.

 [20/23] ("clockevents: purge ->min_delta_ns")
   Corresponds to former
   [19/22] ("clockevents: purge ->min_delta_ns and ->max_delta_ns"),
   but with ->max_delta_ns being kept.

 [21/23] ("clockevents: initial support for mono to raw time conversion")
   Former [20/22] with the following changes:
   - Don't adjust mult for those ced's that have CLOCK_EVT_FEAT_NO_ADJUST set.
   - Don't meld __clockevents_update_bounds() into __clockevents_adjust_freq()
     anymore: the bounds for those devices having CLOCK_EVT_FEAT_NO_ADJUST set
     must have got their bounds set as well.
   - In __clockevents_calc_adjust_freq(), make sure that the adjusted mult
     doesn't exceed the original by more than 12.5%. C.f. [14/23].
   - In timekeeping, define timekeeping_get_mono_mult() only for
     CONFIG_GENERIC_CLOCKEVENTS=y.

  [22/23] ("clockevents: make setting of ->mult and ->mult_adjusted atomic")
   Former [12/22], but with the description updated: previously, it said that
   this patch would introduce a new locking dependency. This is not true.

  [23/23] ("timekeeping: inform clockevents about freq adjustments")
    Former [22/22] with the following changes:
    - Don't adjust mult for those ced's that have CLOCK_EVT_FEAT_NO_ADJUST set.
    - In clockevents_adjust_all_freqs(), reuse the adjusted cached mult only
      if the associated ->shift also matches.
    - Introduce noop clockevents_adjust_all_freqs() in order to fix a
      compilation error with CONFIG_GENERIC_CLOCKEVENTS=n.

Nicolai Stange (23):
  clocksource: sh_cmt: compute rate before registration again
  clocksource: sh_tmu: compute rate before registration again
  clocksource: em_sti: split clock prepare and enable steps
  clocksource: em_sti: compute rate before registration
  clocksource: h8300_timer8: don't reset rate in ->set_state_oneshot()
  clockevents: make clockevents_config() static
  many clockevent drivers: set ->min_delta_ticks and ->max_delta_ticks
  arch/s390/kernel/time: set ->min_delta_ticks and ->max_delta_ticks
  arch/x86/platform/uv/uv_time: set ->min_delta_ticks and
    ->max_delta_ticks
  arch/tile/kernel/time: set ->min_delta_ticks and ->max_delta_ticks
  clockevents: always initialize ->min_delta_ns and ->max_delta_ns
  many clockevent drivers: don't set ->min_delta_ns and ->max_delta_ns
  clockevents: introduce CLOCK_EVT_FEAT_NO_ADJUST flag
  clockevents: decouple ->max_delta_ns from ->max_delta_ticks
  clockevents: do comparison of delta against minimum in terms of cycles
  clockevents: clockevents_program_min_delta(): don't set ->next_event
  clockevents: use ->min_delta_ticks_adjusted to program minimum delta
  clockevents: min delta increment: calculate min_delta_ns from ticks
  timer_list: print_tickdevice(): calculate ->min_delta_ns dynamically
  clockevents: purge ->min_delta_ns
  clockevents: initial support for mono to raw time conversion
  clockevents: make setting of ->mult and ->mult_adjusted atomic
  timekeeping: inform clockevents about freq adjustments

 arch/avr32/kernel/time.c                          |   4 +-
 arch/blackfin/kernel/time-ts.c                    |   8 +-
 arch/c6x/platforms/timer64.c                      |   4 +-
 arch/hexagon/kernel/time.c                        |   4 +-
 arch/m68k/coldfire/pit.c                          |   6 +-
 arch/microblaze/kernel/timer.c                    |   6 +-
 arch/mips/alchemy/common/time.c                   |   4 +-
 arch/mips/jz4740/time.c                           |   4 +-
 arch/mips/kernel/cevt-bcm1480.c                   |   4 +-
 arch/mips/kernel/cevt-ds1287.c                    |   4 +-
 arch/mips/kernel/cevt-gt641xx.c                   |   4 +-
 arch/mips/kernel/cevt-sb1250.c                    |   4 +-
 arch/mips/kernel/cevt-txx9.c                      |   5 +-
 arch/mips/loongson32/common/time.c                |   4 +-
 arch/mips/loongson64/common/cs5536/cs5536_mfgpt.c |   4 +-
 arch/mips/loongson64/loongson-3/hpet.c            |   4 +-
 arch/mips/ralink/cevt-rt3352.c                    |   4 +-
 arch/mips/sgi-ip27/ip27-timer.c                   |   4 +-
 arch/mn10300/kernel/cevt-mn10300.c                |   4 +-
 arch/powerpc/kernel/time.c                        |   6 +-
 arch/s390/kernel/time.c                           |   4 +-
 arch/score/kernel/time.c                          |   6 +-
 arch/sparc/kernel/time_32.c                       |   4 +-
 arch/sparc/kernel/time_64.c                       |   6 +-
 arch/tile/kernel/time.c                           |   4 +-
 arch/um/kernel/time.c                             |   4 +-
 arch/unicore32/kernel/time.c                      |   6 +-
 arch/x86/kernel/apic/apic.c                       |  12 +-
 arch/x86/lguest/boot.c                            |   4 +-
 arch/x86/platform/uv/uv_time.c                    |   6 +-
 arch/x86/xen/time.c                               |   8 +-
 drivers/clocksource/dw_apb_timer.c                |   5 +-
 drivers/clocksource/em_sti.c                      |  49 +++--
 drivers/clocksource/h8300_timer8.c                |   8 -
 drivers/clocksource/metag_generic.c               |   4 +-
 drivers/clocksource/numachip.c                    |   4 +-
 drivers/clocksource/sh_cmt.c                      |  50 ++---
 drivers/clocksource/sh_tmu.c                      |  26 +--
 drivers/clocksource/timer-atlas7.c                |   4 +-
 include/linux/clockchips.h                        |  21 +-
 kernel/time/clockevents.c                         | 221 ++++++++++++++++++----
 kernel/time/tick-broadcast-hrtimer.c              |   2 -
 kernel/time/tick-internal.h                       |   6 +
 kernel/time/timekeeping.c                         |  19 ++
 kernel/time/timer_list.c                          |   9 +-
 45 files changed, 379 insertions(+), 204 deletions(-)

-- 
2.9.3