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Re: [Qemu-devel] [Qemu-arm] [PATCH v5 17/17] target/arm: Rely on hflags
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [Qemu-arm] [PATCH v5 17/17] target/arm: Rely on hflags correct in cpu_get_tb_cpu_state |
Date: |
Thu, 05 Sep 2019 16:50:20 +0100 |
User-agent: |
mu4e 1.3.4; emacs 27.0.50 |
Laurent Desnogues <address@hidden> writes:
> On Thu, Sep 5, 2019 at 5:24 PM Alex Bennée <address@hidden> wrote:
>>
>>
>> Richard Henderson <address@hidden> 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 <address@hidden>
>>
>> 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 <address@hidden>
>> > Signed-off-by: Richard Henderson <address@hidden>
>> > ---
>> > 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