| Message ID | 000601d27ba1$1f009a50$5d01cef0$@ru (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 31/01/2017 01:05, Pavel Dovgalyuk wrote: > 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; So is this needed to avoid exceptions in tb_find? Please add a comment about this and check if you can also replace: atomic_set(&cpu->exit_request, 1); in cpu_loop_exec_tb with cpu->icount_decr.u16.low = 0; ? Thanks, Paolo > Pavel Dovgalyuk > >> -----Original Message----- >> From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo Bonzini >> Sent: Monday, January 30, 2017 12:09 AM >> To: qemu-devel@nongnu.org >> Cc: serge.fdrv@gmail.com; peter.maydell@linaro.org; pavel.dovgaluk@ispras.ru >> 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 > > > >
> From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo Bonzini > On 31/01/2017 01:05, Pavel Dovgalyuk wrote: > > 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; > > So is this needed to avoid exceptions in tb_find? Please add a comment > about this This code comes from my last patch, that was not applied. Here is the comment: It adds check to break cpu loop when icount expires without setting the TB_EXIT_ICOUNT_EXPIRED flag. It happens when there is no available translated blocks and all instructions were executed. In icount replay mode unnecessary tb_find will be called (which may cause an exception) and execution will be non-deterministic. > and check if you can also replace: > > atomic_set(&cpu->exit_request, 1); > > in cpu_loop_exec_tb with > > cpu->icount_decr.u16.low = 0; > > ? > This line is not needed at all, because the following code decrements icount automatically. if (insns_left > 0) { cpu_exec_nocache(cpu, insns_left, tb, false); } Pavel Dovgalyuk
----- Original Message ----- > From: "Pavel Dovgalyuk" <dovgaluk@ispras.ru> > To: "Paolo Bonzini" <pbonzini@redhat.com>, qemu-devel@nongnu.org > Cc: "serge fdrv" <serge.fdrv@gmail.com>, "pavel dovgaluk" <pavel.dovgaluk@ispras.ru>, "peter maydell" > <peter.maydell@linaro.org> > Sent: Thursday, February 2, 2017 11:07:12 PM > Subject: RE: [RFC/RFT PATCH 0/7] cpu-exec: simplify cpu_exec and remove some icount special cases > > > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo > > Bonzini > > On 31/01/2017 01:05, Pavel Dovgalyuk wrote: > > > 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; > > > > So is this needed to avoid exceptions in tb_find? Please add a comment > > about this > > This code comes from my last patch, that was not applied. > Here is the comment: > > It adds check to break cpu loop when icount expires without > setting the TB_EXIT_ICOUNT_EXPIRED flag. It happens when there is no > available translated blocks and all instructions were executed. > In icount replay mode unnecessary tb_find will be called (which may > cause an exception) and execution will be non-deterministic. > > > and check if you can also replace: > > > > atomic_set(&cpu->exit_request, 1); > > > > in cpu_loop_exec_tb with > > > > cpu->icount_decr.u16.low = 0; > > > > ? > > > > This line is not needed at all, because the following code decrements > icount automatically. > > if (insns_left > 0) { > cpu_exec_nocache(cpu, insns_left, tb, false); > } Right, so please send a patch and we can apply my series + yours. Paolo
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;