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

[Pavel Dovgalyuk]

Hi, Paolo!

Thanks for refactoring.
I tested these patches with icount record/replay on i386 machine.
It works, but the following changes should be applied.
I also removed call to replay_has_interrupt, because now it is not needed here.
It seems, that this call is an artifact of an older record/replay revision.

diff --git a/cpu-exec.c b/cpu-exec.c
index 3838eb8..5cef8bc 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -519,7 +519,8 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
     }

     /* Finally, check if we need to exit to the main loop.  */
-    if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) {
+    if (unlikely(atomic_read(&cpu->exit_request)
+        || (use_icount && cpu->icount_decr.u16.low + cpu->icount_extra == 0))) 
{
         atomic_set(&cpu->exit_request, 0);
         cpu->exception_index = EXCP_INTERRUPT;
         return true;

Pavel Dovgalyuk

> -----Original Message-----
> From: Paolo Bonzini [mailto:address@hidden On Behalf Of Paolo Bonzini
> Sent: Monday, January 30, 2017 12:09 AM
> To: address@hidden
> Cc: address@hidden; address@hidden; address@hidden
> Subject: [RFC/RFT PATCH 0/7] cpu-exec: simplify cpu_exec and remove some 
> icount special cases
> 
> 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.
> 
> 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(-)
> 
> --
> 2.9.3