Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenariosin PLE handler

[Andrew Jones]

On Wed, Sep 26, 2012 at 03:26:11PM +0200, Peter Zijlstra wrote:
> On Wed, 2012-09-26 at 15:20 +0200, Andrew Jones wrote:
> > Wouldn't a clean solution be to promote a task's scheduler
> > class to the spinner class when we PLE (or come from some special
> > syscall
> > for userspace spinlocks?)? 
> 
> Userspace spinlocks are typically employed to avoid syscalls..

I'm guessing there could be a slow path - spin N times and then give
up and yield.

> 
> > That class would be higher priority than the
> > fair class and would schedule in FIFO order, but it would only run its
> > tasks for short periods before switching. 
> 
> Since lock hold times aren't limited, esp. for things like userspace
> 'spin' locks, you've got a very good denial of service / opportunity for
> abuse right there.

Maybe add some throttling to avoid overuse/maliciousness?

> 
> 
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