Re: sched=null vwfi=native and call_rcu()

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Mon, 2022-01-17 at 12:13 +0100, Juergen Gross wrote:
> On 17.01.22 12:05, George Dunlap wrote:
> > 
> > An x86 equivalent of vwfi=native could be implemented easily, but
> > AFAIK nobody has asked for it yet.  I agree that we need to fix if
> > for ARM, and so in the absence of someone with the time to fix up
> > the x86 side, I think fixing ARM-only is the way to go.
> > 
> > It would be good if we could add appropriate comments warning
> > anyone who implements `hlt=native` on x86 the problems they’ll face
> > and how to fix them.  Not sure the best place to do that; in the
> > VMX / SVM code that sets the exit for HLT &c?
> 
> But wouldn't a guest in a busy loop on x86 with NULL scheduler suffer
> from the same problem?
> 
Right, and even more 'idle=poll' as a _guest_ kernel command line
parameter, IMO.

That does not change what happens when the guest issue an HLT, but it
drastically reduces the frequency of it doing so (or at least, it did
the last time I tried it).

So it's not exactly like wfi=native on ARM, but on the other hand, it
can be under the guest's control.

> And wouldn't that be a problem for PV guests, too?
> 
Yeah, that's one of the things that makes it tricky

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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