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From: Peter Maydell <peter.maydell@linaro.org>
Date: Mon, 15 Jun 2015 16:49:03 +0100
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Subject: Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main
 loop event // how to improve IPI latency?
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To: =?UTF-8?Q?Alex_Z=C3=BCpke?= <alexander.zuepke@hs-rm.de>
Cc: QEMU Developers <qemu-devel@nongnu.org>

On 15 June 2015 at 16:36, Alex Z=C3=BCpke <alexander.zuepke@hs-rm.de> wrote=
:
> So this is the way to go:
>
> --- a/target-arm/translate.c
> +++ b/target-arm/translate.c
> @@ -4084,6 +4084,7 @@ static void gen_nop_hint(DisasContext *s, int val)
>          gen_set_pc_im(s, s->pc);
>          s->is_jmp =3D DISAS_WFI;
>          break;
> +    case 1: /* yield */
>      case 2: /* wfe */
>          gen_set_pc_im(s, s->pc);
>          s->is_jmp =3D DISAS_WFE;

Actually I want to split out the yield code path from the wfe
one, because some day we may actually implement WFE as WFE,
at which point WFE has some trap-to-EL2 logic that YIELD
doesn't. I was about to write a patch to do that...

(If you plan to run your custom OS under a hypervisor you
might prefer SEV/WFE over YIELD, because then if your custom OS
is under heavy load the hypervisor has a chance to swap this
vcpu out and run some other one.)

thanks
-- PMM