Re: [Xen-devel] Can Xen sleep or wake up a thread?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-10-09 at 12:15 +0100, George Dunlap wrote:
> On Tue, Oct 8, 2013 at 4:11 PM, Xinxin Jin <xinxinjin89@xxxxxxxxx> wrote:
> > Hi everyone,
> >
> > I found in Xen, when synchronization between multiple threads is needed, Xen
> > always uses busy wait or simple spin lock. In linux, the kernel can block a
> > waiting thread and schedule other threads for execution. Why does Xen do not
> > have this mechanism? I guess it is because the performance issue? A lot of
> > appreciation for your answer !!
> 
> Linux keeps per-thread kernel stacks, so it can call schedule() and
> block in the middle of kernel code.  Xen does not keep per-vcpu
> hypervisor stacks, so in general it cannot block in the middle of
> hypervisor code.

And since it does not deal with e.g. I/O which can take a long time
there is typically no need for the hypervisor to block anyway.

Ian.


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