Re: [RFC v3 0/8] QEMU cpus.c refactoring part2

[Claudio Fontana <cfontana@suse.de>]

On 8/3/20 1:48 PM, Alex Bennée wrote:
> 
> Claudio Fontana <cfontana@suse.de> writes:
> 
>> Motivation and higher level steps:
>>
>> https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg04628.html
>>
>> The biggest open item for me is, does it makes sense to:
>>
>>
>> 1) make icount TCG-only (building the icount module only under
>> CONFIG_TCG), as this series suggests, and provide a separate virtual
>> counter for qtest,
> 
> Well icount certainly never has any use except with TCG - the fields are
> all wasted in the KVM case.
> 
>> or
>>
>>
>> 2) continue to keep icount functions and fields, including vmstate,
>> in all softmmu builds because of qtest current use of field
>> qemu_icount_bias to implement its virtual counter for
>> qtest_clock_warp?
> 
> Is this just a case of maintaining compatibility for saved VM images? We
> could certainly keep the fields in VM state and stub out (or warn?) if a
> icount related field turned up when reloading a VM into a KVM only build
> or a build with !tcg_enabled().
> 
> I would defer to the vmstate experts on the best way to do this? Is the
> field currently unconditional? Certainly the rr bits are only registered
> when RR is enabled.


Hi Alex and all,

do we have a compatibility issue to worry about?

Ie, I assumed looking at the "needed" functions in vmstate that
if a VM contains a subfield that is unneeded when loaded, it would just be ignored.

But maybe this was a too optimistic assumption?

Thank you,

Claudio


> 
>> If I understand correctly Paolo might be for 2) (?)
>> would also welcome additional input from the community in any direction
>> (Alex, Peter, Philippe?)
>>
>> ----
>>
>> RFC v2 -> v3:
>>
>> * provided defaults for all methods.
>>   Only create_vcpu_thread is now a mandatory field. (Paolo)
>>
>> * separated new CpusAccel patch from its first user, new patch nr. 2:
>>   "cpus: prepare new CpusAccel cpu accelerator interface"
>>
>> * new CpusAccel methods: get_virtual_clock and get_elapsed_ticks.
>>   (Paolo)
>>
>>   In this series, get_virtual_clock has a separate implementation
>>   between TCG/icount and qtest,
>>   while get_elapsed_ticks only returns a virtual counter for icount.
>>
>>   Looking for more comments in this area.
>>
>> ----
>>
>> RFC v1 -> v2:
>>
>> * split the cpus.c accelerator refactoring into 6 patches.
>>
>> * other minor changes to be able to proceed step by step.
>>
>> ----
>>
>> * Rebased on commit 255ae6e2158c743717bed76c9a2365ee4bcd326e,
>> "replay: notify the main loop when there are no instructions"
>>
>> [SPLIT into part1 and part2]
>>
>> ----
>>
>> v6 -> v7:
>>
>> * rebased changes on top of Pavel Dovgalyuk changes to dma-helpers.c
>>   "icount: make dma reads deterministic"
>>
>> ----
>>
>> v5 -> v6:
>>
>> * rebased changes on top of Emilio G. Cota changes to cpus.c
>>   "cpu: convert queued work to a QSIMPLEQ"
>>
>> * keep a pointer in cpus.c instead of a copy of CpusAccel
>>   (Alex)
>>
>> ----
>>
>>
>> v4 -> v5: rebase on latest master
>>
>> * rebased changes on top of roman series to remove one of the extra states for hvf.
>>   (Is the result now functional for HVF?)
>>
>> * rebased changes on top of icount changes and fixes to icount_configure and
>>   the new shift vmstate. (Markus)
>>
>> v3 -> v4:
>>
>> * overall: added copyright headers to all files that were missing them
>>   (used copyright and license of the module the stuff was extracted from).
>>   For the new interface files, added SUSE LLC.
>>
>> * 1/4 (move softmmu only files from root):
>>
>>   MAINTAINERS: moved softmmu/cpus.c to its final location (from patch 2)
>>
>> * 2/4 (cpu-throttle):
>>
>>   MAINTAINERS (to patch 1),
>>   copyright Fabrice Bellard and license from cpus.c
>>
>> * 3/4 (cpu-timers, icount):
>>
>>   - MAINTAINERS: add cpu-timers.c and icount.c to Paolo
>>
>>   - break very long lines (patchew)
>>
>>   - add copyright SUSE LLC, GPLv2 to cpu-timers.h
>>
>>   - add copyright Fabrice Bellard and license from cpus.c to timers-state.h
>>     as it is lifted from cpus.c
>>
>>   - vl.c: in configure_accelerators bail out if icount_enabled()
>>     and !tcg_enabled() as qtest does not enable icount anymore.
>>
>> * 4/4 (accel stuff to accel):
>>
>>   - add copyright SUSE LLC to files that mostly only consist of the
>>     new interface. Add whatever copyright was in the accelerator code
>>     if instead they mostly consist of accelerator code.
>>
>>   - change a comment to mention the result of the AccelClass experiment
>>
>>   - moved qtest accelerator into accel/qtest/ , make it like the others.
>>
>>   - rename xxx-cpus-interface to xxx-cpus (remove "interface" from names)
>>
>>   - rename accel_int to cpus_accel
>>
>>   - rename CpusAccel functions from cpu_synchronize_* to synchronize_*
>>
>>
>> --------
>>
>> v2 -> v3:
>>
>> * turned into a 4 patch series, adding a first patch moving
>>   softmmu code currently in top_srcdir to softmmu/
>>
>> * cpu-throttle: moved to softmmu/
>>
>> * cpu-timers, icount:
>>
>>   - moved to softmmu/
>>
>>   - fixed assumption of qtest_enabled() => icount_enabled()
>>   causing the failure of check-qtest-arm goal, in test-arm-mptimer.c
>>
>>   Fix is in hw/core/ptimer.c,
>>
>>   where the artificial timeout rate limit should not be applied
>>   under qtest_enabled(), in a similar way to how it is not applied
>>   for icount_enabled().
>>
>> * CpuAccelInterface: no change.
>>
>>
>> --------
>>
>>
>> v1 -> v2:
>>
>> * 1/3 (cpu-throttle): provide a description in the commit message
>>
>> * 2/3 (cpu-timers, icount): in this v2 separate icount from cpu-timers,
>>   as icount is actually TCG-specific. Only build it under CONFIG_TCG.
>>
>>   To do this, qtest had to be detached from icount. To this end, a
>>   trivial global counter for qtest has been introduced.
>>
>> * 3/3 (CpuAccelInterface): provided a description.
>>
>> This is point 8) in that plan. The idea is to extract the unrelated parts
>> in cpus, and register interfaces from each single accelerator to the main
>> cpus module (cpus.c).
>>
>> While doing this RFC, I noticed some assumptions about Windows being
>> either TCG or HAX (not considering WHPX) that might need to be revisited.
>> I added a comment there.
>>
>> The thing builds successfully based on Linux cross-compilations for
>> windows/hax, windows/whpx, and I got a good build on Darwin/hvf.
>>
>> Tests run successully for tcg and kvm configurations, but did not test on
>> windows or darwin.
>>
>> Welcome your feedback and help on this,
>>
>> Claudio
>>
>> Claudio Fontana (8):
>>   cpu-timers, icount: new modules
>>   cpus: prepare new CpusAccel cpu accelerator interface
>>   cpus: extract out TCG-specific code to accel/tcg
>>   cpus: extract out qtest-specific code to accel/qtest
>>   cpus: extract out kvm-specific code to accel/kvm
>>   cpus: extract out hax-specific code to target/i386/
>>   cpus: extract out whpx-specific code to target/i386/
>>   cpus: extract out hvf-specific code to target/i386/hvf/
>>
>>  MAINTAINERS                    |    5 +-
>>  accel/Makefile.objs            |    2 +-
>>  accel/kvm/Makefile.objs        |    2 +
>>  accel/kvm/kvm-all.c            |   14 +-
>>  accel/kvm/kvm-cpus.c           |   88 +++
>>  accel/kvm/kvm-cpus.h           |   17 +
>>  accel/qtest/Makefile.objs      |    2 +
>>  accel/qtest/qtest-cpus.c       |   91 +++
>>  accel/qtest/qtest-cpus.h       |   17 +
>>  accel/{ => qtest}/qtest.c      |   13 +-
>>  accel/stubs/kvm-stub.c         |    3 +-
>>  accel/tcg/Makefile.objs        |    1 +
>>  accel/tcg/cpu-exec.c           |   43 +-
>>  accel/tcg/tcg-all.c            |   19 +-
>>  accel/tcg/tcg-cpus.c           |  541 +++++++++++++
>>  accel/tcg/tcg-cpus.h           |   17 +
>>  accel/tcg/translate-all.c      |    3 +-
>>  dma-helpers.c                  |    4 +-
>>  docs/replay.txt                |    6 +-
>>  exec.c                         |    4 -
>>  hw/core/cpu.c                  |    1 +
>>  hw/core/ptimer.c               |    8 +-
>>  hw/i386/x86.c                  |    3 +-
>>  include/exec/cpu-all.h         |    4 +
>>  include/exec/exec-all.h        |    4 +-
>>  include/qemu/timer.h           |   24 +-
>>  include/sysemu/cpu-timers.h    |   84 ++
>>  include/sysemu/cpus.h          |   48 +-
>>  include/sysemu/hw_accel.h      |   69 +-
>>  include/sysemu/kvm.h           |    2 +-
>>  include/sysemu/qtest.h         |    2 +
>>  include/sysemu/replay.h        |    4 +-
>>  replay/replay.c                |    6 +-
>>  softmmu/Makefile.objs          |    2 +
>>  softmmu/cpu-timers.c           |  279 +++++++
>>  softmmu/cpus.c                 | 1661 +++-------------------------------------
>>  softmmu/icount.c               |  497 ++++++++++++
>>  softmmu/qtest.c                |   34 +-
>>  softmmu/timers-state.h         |   69 ++
>>  softmmu/vl.c                   |   11 +-
>>  stubs/Makefile.objs            |    6 +-
>>  stubs/clock-warp.c             |    7 -
>>  stubs/cpu-get-clock.c          |    3 +-
>>  stubs/cpu-get-icount.c         |   21 -
>>  stubs/cpu-synchronize-state.c  |   15 +
>>  stubs/cpus-get-virtual-clock.c |    8 +
>>  stubs/icount.c                 |   52 ++
>>  stubs/qemu-timer-notify-cb.c   |    8 +
>>  stubs/qtest.c                  |    5 +
>>  target/alpha/translate.c       |    3 +-
>>  target/arm/helper.c            |    7 +-
>>  target/i386/Makefile.objs      |    7 +-
>>  target/i386/hax-all.c          |    6 +-
>>  target/i386/hax-cpus.c         |   85 ++
>>  target/i386/hax-cpus.h         |   17 +
>>  target/i386/hax-i386.h         |    2 +
>>  target/i386/hax-posix.c        |   12 +
>>  target/i386/hax-windows.c      |   20 +
>>  target/i386/hvf/Makefile.objs  |    2 +-
>>  target/i386/hvf/hvf-cpus.c     |  131 ++++
>>  target/i386/hvf/hvf-cpus.h     |   17 +
>>  target/i386/hvf/hvf.c          |    3 +
>>  target/i386/whpx-all.c         |    3 +
>>  target/i386/whpx-cpus.c        |   96 +++
>>  target/i386/whpx-cpus.h        |   17 +
>>  target/riscv/csr.c             |    8 +-
>>  tests/ptimer-test-stubs.c      |    7 +-
>>  tests/test-timed-average.c     |    2 +-
>>  util/main-loop.c               |   12 +-
>>  util/qemu-timer.c              |   14 +-
>>  70 files changed, 2528 insertions(+), 1772 deletions(-)
>>  create mode 100644 accel/kvm/kvm-cpus.c
>>  create mode 100644 accel/kvm/kvm-cpus.h
>>  create mode 100644 accel/qtest/Makefile.objs
>>  create mode 100644 accel/qtest/qtest-cpus.c
>>  create mode 100644 accel/qtest/qtest-cpus.h
>>  rename accel/{ => qtest}/qtest.c (81%)
>>  create mode 100644 accel/tcg/tcg-cpus.c
>>  create mode 100644 accel/tcg/tcg-cpus.h
>>  create mode 100644 include/sysemu/cpu-timers.h
>>  create mode 100644 softmmu/cpu-timers.c
>>  create mode 100644 softmmu/icount.c
>>  create mode 100644 softmmu/timers-state.h
>>  delete mode 100644 stubs/clock-warp.c
>>  delete mode 100644 stubs/cpu-get-icount.c
>>  create mode 100644 stubs/cpu-synchronize-state.c
>>  create mode 100644 stubs/cpus-get-virtual-clock.c
>>  create mode 100644 stubs/icount.c
>>  create mode 100644 stubs/qemu-timer-notify-cb.c
>>  create mode 100644 target/i386/hax-cpus.c
>>  create mode 100644 target/i386/hax-cpus.h
>>  create mode 100644 target/i386/hvf/hvf-cpus.c
>>  create mode 100644 target/i386/hvf/hvf-cpus.h
>>  create mode 100644 target/i386/whpx-cpus.c
>>  create mode 100644 target/i386/whpx-cpus.h
> 
>