Re: [Qemu-devel] [PATCH] qemu-kvm: response to SIGUSR1 to start/stop a VCPU (v2)

[Anthony Liguori]

On 11/23/2010 01:35 PM, Blue Swirl wrote:
> On Tue, Nov 23, 2010 at 4:49 PM, Anthony Liguori<address@hidden>  wrote:
>    
> > qemu-kvm vcpu threads don't response to SIGSTOP/SIGCONT.  Instead of teaching
> > them to respond to these signals (which cannot be trapped), use SIGUSR1 to
> > approximate the behavior of SIGSTOP/SIGCONT.
> >
> > The purpose of this is to implement CPU hard limits using an external tool that
> > watches the CPU consumption and stops the VCPU as appropriate.
> >
> > This provides a more elegant solution in that it allows the VCPU thread to
> > release qemu_mutex before going to sleep.
> >
> > This current implementation uses a single signal.  I think this is too racey
> > in the long term so I think we should introduce a second signal.  If two signals
> > get coalesced into one, it could confuse the monitoring tool into giving the
> > VCPU the inverse of it's entitlement.
> >
> > It might be better to simply move this logic entirely into QEMU to make this
> > more robust--the question is whether we think this is a good long term feature
> > to carry in QEMU?
> >      
>    
> > +static __thread int sigusr1_wfd;
> >      
> While OpenBSD finally updated the default compiler to 4.2.1 from 3.x
> series, thread local storage is still not supported:
>    

Hrm, is there a portable way to do this (distinguish a signal on a 
particular thread)?

Regards,

Anthony Liguori

> $ cat thread.c
> static __thread int sigusr1_wfd;
> $ gcc thread.c -c
> thread.c:1: error: thread-local storage not supported for this target
> $ gcc -v
> Reading specs from /usr/lib/gcc-lib/sparc64-unknown-openbsd4.8/4.2.1/specs
> Target: sparc64-unknown-openbsd4.8
> Configured with: OpenBSD/sparc64 system compiler
> Thread model: posix
> gcc version 4.2.1 20070719
>