Re: [Qemu-devel] [RFC/RFT PATCH 0/7] cpu-exec: simplify cpu_exec and remove some icount special cases

[Paolo Bonzini]

On 15/02/2017 13:45, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:address@hidden On Behalf Of Paolo Bonzini
>> On 29/01/2017 22:09, Paolo Bonzini wrote:
>>> The series includes three parts:
>>>
>>> 1-2: fix two bugs, the first one pretty bad, the second seems
>>> to be theoretical only.
>>>
>>> 3-5: simplify cpu_exec.  This builds on Sergey's conversion
>>> of cpu_exec to a simple top-down logic, making the phases
>>> clearer and saving on the cost of siglongjmp in the meanwhile.
>>
>> I'll include these five in my next pull request.  Review for patch 6 is
>> welcome!
> 
> I've tested all 7 and briefly looked at their code.
> Do you need official reviewed-by?

No, but for patch 6 specifically, I would like more than one review. :)

Paolo

> Pavel Dovgalyuk
>>
>>> 6-7: these are intended to be a base for Pavel's record/replay
>>> fixes.  The main thing I noticed while reviewing is that icount
>>> is redoing (with u16.high) a lot of things that tcg_exit_req is
>>> doing too.  This is because, at the time icount was introduced,
>>> tcg_exit_req didn't exist and QEMU instead unwound chained TBs
>>> through POSIX signals.  But now we have essentially two ways to
>>> do the same thing with subtly different invariants or downright
>>> bugs (such as the one fixed by patch 1).  Patch 6 therefore
>>> unifies tcg_exit_req and the icount interrupt flag.  It saves a
>>> handful of instructions per TB in icount mode and generally
>>> makes icount mode "less special", which is a good thing since
>>> no one seems to understand it well.  Patch 7 then removes another
>>> EXCP_INTERRUPT/cpu_loop_exit pair; by exiting to main loop simply
>>> through cpu->exit_request, hopefully it fixes one of the issues that
>>> Pavel was seeing.
>>>
>>> For now I've tested this only on an aarch64 Linux image (with
>>> and without -icount).  Thanks,
>>>
>>> Paolo
>>>
>>> Paolo Bonzini (7):
>>>   cpu-exec: fix jmp_first out-of-bounds access with icount
>>>   cpu-exec: tighten barrier on TCG_EXIT_REQUESTED
>>>   cpu-exec: avoid cpu_loop_exit in cpu_handle_interrupt
>>>   cpu-exec: avoid repeated sigsetjmp on interrupts
>>>   cpu-exec: remove outermost infinite loop
>>>   cpu-exec: unify icount_decr and tcg_exit_req
>>>   cpu-exec: centralize exiting to the main loop
>>>
>>>  cpu-exec.c                | 153 
>>> +++++++++++++++++++++-------------------------
>>>  include/exec/exec-all.h   |   1 +
>>>  include/exec/gen-icount.h |  53 ++++++++--------
>>>  include/qom/cpu.h         |  15 +++--
>>>  qom/cpu.c                 |   2 +-
>>>  tcg/tcg.h                 |   1 -
>>>  translate-all.c           |   2 +-
>>>  translate-common.c        |  13 ++--
>>>  8 files changed, 109 insertions(+), 131 deletions(-)
>>>
>