Re: [Qemu-devel] [PATCH] vl.c: make default main_loop_wait() timeout independed of slirp

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jun 05, 2018 at 10:27:03AM +0200, Igor Mammedov wrote:
> On Mon, 4 Jun 2018 22:04:13 -0300
> Eduardo Habkost <ehabkost@redhat.com> wrote:
> 
> > On Mon, Jun 04, 2018 at 10:14:38PM +0200, Igor Mammedov wrote:
> > > Since commit (047f7038f58 cli: add --preconfig option) QEMU is
> > > stuck with indefinite timeout in os_host_main_loop_wait()
> > > at RUN_STATE_PRECONFIG even if --preconfig option wasn't used
> > > when it's started with -nodefaults CLI option like this:
> > > 
> > >   ./s390x-softmmu/qemu-system-s390x -nodefaults
> > > 
> > > It's caused by the fact that slirp_pollfds_fill() bails out early
> > > and slirp_update_timeout() won't be called to update timeout
> > > to a reasonable value (1 sec) so timeout would be left with
> > > infinite value (0xFFFFFFFF).
> > > 
> > > Default infinite timeout though doen't make sense and reducing
> > > it to 1 second as in slirp_update_timeout() won't affect host.  
> > 
> > I don't get this part.  Why default infinite timeout doesn't make
> > sense?  Why would a 1 second timeout make sense?
> I've meant that there is no reason for infinite timeuot,
> and 1sec is good as any other finite one.

I don't really agree - it is better to not wakeup at all if there's
no work todo rather than pointlessly wake up once a second, to deal
with a hack for the SLIRP feature that's almost never used in most
production scenarios..

> Hence we can unify timeout with/without -nodefaults, by moving 1sec
> constant from slirp to main_loop_wait() and simplify code a bit.
>  
> > 
> > > Fix issue by simplifying default timeout to the same 1sec as it
> > > is in slirp_update_timeout() and cleanup the later. It makes
> > > default timeout the same regardless of slirp_pollfds_fill()
> > > exited early or not (i.e. -nodefaults won't have any effect on
> > > main_loop_wait() anymore, which would provide more consistent
> > > behavior between both variants of startup).
> > > 
> > > Reported-by: Lukáš Doktor <ldoktor@redhat.com>
> > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > > ---
> > > PS:
> > > it doesn't fix issue reported by Max where
> > >   "echo foo | $QEMU"
> > > is also broken due to commit 047f7038f58, but there is antoher fix
> > > on the list to fix that (either Michal's or Daniel's).  
> > [...]
> > 
> 
> 

Regards,
Daniel
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