Re: [Qemu-devel] [PATCH v2 6/8] cpu: make CPU_INTERRUPT_RESET available on all targets

[Peter Maydell]

On 24 May 2014 13:59, Paolo Bonzini <address@hidden> wrote:
> Il 24/05/2014 10:30, Peter Maydell ha scritto:
>> Well, I'm planning to move the bodies of all the ifdefs into
>> a cpu_check_interrupts() provided by the target's cpu.h[*].
>> This x86 bit is just awkward because it means there's
>> x86 stuff both before and after the generic reset code.
>
> What about
>
>         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
>             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
>             cpu->exception_index = EXCP_DEBUG;
>             cpu_loop_exit(cpu);
>         }
>         if (!cpu_check_interrupts(...)) {
>             if (interrupt_request & CPU_INTERRUPT_HALT) {
>                 cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
>                 cpu->halted = 1;
>                 cpu->exception_index = EXCP_HLT;
>                 cpu_loop_exit(cpu);
>             }
>             if (interrupt_request & CPU_INTERRUPT_RESET) {
>                 cpu_reset(cpu);
>             }
>         }
>
> Then:
> - only X86 returns 1 for CPU_INTERRUPT_RESET
> - all except ARM/SPARC/MIPS/PPC/Alpha/cris/MicroBlaze/LM32/Unicore32
> return 1 for CPU_INTERRUPT_HALT

That last point sounds wrong, at least -- halt should work
the same way for everything. If the target doesn't want
to halt it should never set the HALT bit in interrupt_request.

>> [*] not a cpu method since it seemed like it would be
>> a bad idea to have a function pointer call every
>> time round the main loop when there's a blocked
>> interrupt...
>
> We have that already for cc->do_interrupt, which could be
> "devirtualized" if you add a check_interrupts method...  In
> the end you'd be adding a function pointer call for all
> interrupt requests but removing one for CPU_INTERRUPT_HARD
> (and FIQ too on ARM).  That should be a wash.

But we only call cc->do_interrupt if we're going to actually
*take* an interrupt, in which case the bulk of the cost is
actually doing the work. I don't want to call via a pointer
just for the other end to say "actually PSTATE_I is set
because the guest has interrupts blocked, so don't do
anything".

thanks
-- PMM