Re: [PATCH v2 2/2] x86/xen: allow privcmd hypercalls to be preempted

Luis R. Rodriguez
2014-12-11T20:39:26Z

On Thu, Dec 11, 2014 at 10:47:44AM -0800, H. Peter Anvin wrote:
> On 12/10/2014 05:03 PM, Luis R. Rodriguez wrote:
> >
> > This is an issue onloy for for non*-preemptive kernels.
> >
> > Some of Xen's hypercalls can take a long time and unfortunately for
> > *non*-preemptive kernels this can be quite a bit of an issue.
> > We've handled situations like this with cond_resched() before which will
> > push even *non*-preemptive kernels to behave as voluntarily preemptive,
> > I was not aware to what extent this was done and precedents set but
> > its pretety widespread now... this then just addresses once particular
> > case where this is also an issuefor but now in IRQ context.
> >
> > I agree its a hack but so are all the other cond_reshed() calls then.
> > I don't think its a good idea to be spreading use of something like
> > this everywhere but after careful review and trying toa void this
> > exact code for a while I have not been able to find any other reasonable
> > alternative.
> >
>
> This sounds like a patch that is completely unrelated to the rest of the
> patch.

If you mean architecture and design then yes however this patch tries
to look for a resolution with the existing architecture.

Luis