Re: [Qemu-devel] [RFC v1 4/4] util/oslib-win32: Recursivly pass the timeout

[Paolo Bonzini <pbonzini@redhat.com>]

> On Thu, Jun 29, 2017 at 5:34 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> > On 28/06/2017 01:57, Alistair Francis wrote:
> > I'm not sure I agree with this change, which is effectively delaying the
> > processing of events.  The question to me is which handles are
> > triggering so fast that QEMU effectively busy waits.
> 
> Yeah, that is what I was trying to figure out, but didn't make much headway.
> 
> I kept seeing zero timeouts, which means that the thread never blocks
> and this patch helps a lot.

Perhaps you can use tracepoints?  There shouldn't be many handles registered,
since on Windows even the GUI actions all go through messages.

> > Maybe your QEMUs can get some breath with commit 12f8def0e0 ("win32:
> > replace custom mutex and condition variable with native primitives",
> > 2017-03-27), since the native primitives are more efficient and TCG 2.8
> > used condvars a lot for qemu_io_proceeded_cond.
> 
> Ok, I will try that.
> 
> Does this mean you don't see the same slowness on QEMU 2.9?

I have not tried, but the patch is only working around the real issue,
as Fam pointed out.

Paolo