Re: [Qemu-devel] Linux kernel polling for QEMU

[Peter Maydell]

On 29 November 2016 at 19:38, Andrew Jones <address@hidden> wrote:
> Thanks for making me look, I was simply assuming we were in the while
> loops above.
>
> I couldn't get the problem to reproduce with access to the monitor,
> but by adding '-d exec' I was able to see cpu0 was on the wfe in
> smp_boot_secondary. It should only stay there until cpu1 executes the
> sev in secondary_cinit, but it looks like TCG doesn't yet implement sev
>
>  $ grep SEV target-arm/translate.c
>         /* TODO: Implement SEV, SEVL and WFE.  May help SMP performance.

Yes, we currently NOP SEV. We only implement WFE as "yield back
to TCG top level loop", though, so this is fine. The idea is
that WFE gets used in busy loops so it's a helpful hint to
try running some other TCG vCPU instead of just spinning in
the guest on this one. Implementing SEV as a NOP and WFE as
a more-or-less NOP is architecturally permitted (guest code
is required to cope with WFE returning "early"). If something
is not working correctly then it's either buggy guest code
or a problem with the generic TCG scheduling of CPUs.

thanks
-- PMM