Re: [Qemu-devel] [Qemu-arm] [PATCH v5 17/17] target/arm: Rely on hflags correct in cpu_get_tb_cpu_state

["Alex Bennée" <alex.bennee@linaro.org>]

Laurent Desnogues <laurent.desnogues@gmail.com> writes:

> On Thu, Sep 5, 2019 at 5:24 PM Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>>
>> Richard Henderson <richard.henderson@linaro.org> writes:
>>
>> > This is the payoff.
>> >
>> > From perf record -g data of ubuntu 18 boot and shutdown:
>> >
>> > BEFORE:
>> >
>> > -   23.02%     2.82%  qemu-system-aar  [.] helper_lookup_tb_ptr
>> >    - 20.22% helper_lookup_tb_ptr
>> >       + 10.05% tb_htable_lookup
>> >       - 9.13% cpu_get_tb_cpu_state
>> >            3.20% aa64_va_parameters_both
>> >            0.55% fp_exception_el
>> >
>> > -   11.66%     4.74%  qemu-system-aar  [.] cpu_get_tb_cpu_state
>> >    - 6.96% cpu_get_tb_cpu_state
>> >         3.63% aa64_va_parameters_both
>> >         0.60% fp_exception_el
>> >         0.53% sve_exception_el
>> >
>> > AFTER:
>> >
>> > -   16.40%     3.40%  qemu-system-aar  [.] helper_lookup_tb_ptr
>> >    - 13.03% helper_lookup_tb_ptr
>> >       + 11.19% tb_htable_lookup
>> >         0.55% cpu_get_tb_cpu_state
>> >
>> >      0.98%     0.71%  qemu-system-aar  [.] cpu_get_tb_cpu_state
>> >
>> >      0.87%     0.24%  qemu-system-aar  [.] rebuild_hflags_a64
>> >
>> > Before, helper_lookup_tb_ptr is the second hottest function in the
>> > application, consuming almost a quarter of the runtime.  Within the
>> > entire execution, cpu_get_tb_cpu_state consumes about 12%.
>> >
>> > After, helper_lookup_tb_ptr has dropped to the fourth hottest function,
>> > with consumption dropping to a sixth of the runtime.  Within the
>> > entire execution, cpu_get_tb_cpu_state has dropped below 1%, and the
>> > supporting function to rebuild hflags also consumes about 1%.
>> >
>> > Assertions are retained for --enable-debug-tcg.
>> >
>> > Tested-by: Alex Bennée <alex.bennee@linaro.org>
>>
>> Hmm something must have been missed for M-profile because:
>>
>>   make run-tcg-tests-arm-softmmu V=1
>>
>> Leads to:
>>
>>   timeout 15  /home/alex/lsrc/qemu.git/builds/all.debug/arm-softmmu/qemu-system-arm -monitor none -display none -chardev file,path=test-armv6m-undef.out,id=output -semihosting -M microbit -kernel test-armv6m-undef
>>   qemu: fatal: Lockup: can't escalate 3 to HardFault (current priority -1)
>>
>>   R00=00000000 R01=00000000 R02=00000000 R03=00000000
>>   R04=00000000 R05=00000000 R06=00000000 R07=00000000
>>   R08=00000000 R09=00000000 R10=00000000 R11=00000000
>>   R12=00000000 R13=20003fe0 R14=fffffff9 R15=000000c0
>>   XPSR=41000003 -Z-- T handler
>>   FPSCR: 00000000
>>   timeout: the monitored command dumped core
>>
>> But annoyingly not shown up by the debug-tcg verification. The commit
>> before works fine.
>
> There's a typo in the patch:  that should not be CONFIG_TCG_DEBUG but
> CONFIG_DEBUG_TCG.  With this you should see the assert fire.

Indeed:

  cpu_get_tb_cpu_state: cache 110000c0 <> 312000c0

I wish there was an assert form that would handily print out the
difference between the two values. I wonder if glib has one...

>
> I let Richard know that there's an issue with the handling of CPSR E
> flag (BE_DATA in hflags).  I don't know if that applies to your test.
>
> Thanks,
>
> Laurent
>
>> > Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> > ---
>> > v2: Retain asserts for future debugging.
>> > ---
>> >  target/arm/helper.c | 9 ++++++---
>> >  1 file changed, 6 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/target/arm/helper.c b/target/arm/helper.c
>> > index d1bf71a260..5e4f996882 100644
>> > --- a/target/arm/helper.c
>> > +++ b/target/arm/helper.c
>> > @@ -11211,12 +11211,15 @@ void HELPER(rebuild_hflags_a64)(CPUARMState *env, int el)
>> >  void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
>> >                            target_ulong *cs_base, uint32_t *pflags)
>> >  {
>> > -    uint32_t flags, pstate_for_ss;
>> > +    uint32_t flags = env->hflags;
>> > +    uint32_t pstate_for_ss;
>> >
>> >      *cs_base = 0;
>> > -    flags = rebuild_hflags_internal(env);
>> > +#ifdef CONFIG_TCG_DEBUG
>> > +    assert(flags == rebuild_hflags_internal(env));
>> > +#endif
>> >
>> > -    if (is_a64(env)) {
>> > +    if (FIELD_EX32(flags, TBFLAG_ANY, AARCH64_STATE)) {
>> >          *pc = env->pc;
>> >          if (cpu_isar_feature(aa64_bti, env_archcpu(env))) {
>> >              flags = FIELD_DP32(flags, TBFLAG_A64, BTYPE, env->btype);
>>
>>
>> --
>> Alex Bennée
>>


--
Alex Bennée