Il 24/05/2014 17:54, Peter Maydell ha scritto:
On 24 May 2014 13:59, Paolo Bonzini <pbonz...@redhat.com> 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.
Yes, you're right. Those targets simply do not use CPU_INTERRUPT_HALT
to halt the VPU.
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".
Isn't the cost of exiting the translated code (such as the hash table
lookup and qemu_cpu_kick itself) orders of magnitude higher than the
cost of the indirect call?
Furthermore, if this were a problem, you could latch the interrupt when
you get CPU_INTERRUPT_HARD, and trigger it in the instruction that
resets PSTATE_I. This would avoid examining cpu->interrupt_request on
all TB exits between generation of the interrupt and clearing of PSTATE_I.
Paolo
