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Date:	Wed, 26 Sep 2012 15:26:11 +0200
From:	Peter Zijlstra <>
To:	Andrew Jones <>
Cc:	Avi Kivity <>,
	Raghavendra K T <>,
	"H. Peter Anvin" <>,
	Marcelo Tosatti <>,
	Ingo Molnar <>, Rik van Riel <>,
	Srikar <>,
	"Nikunj A. Dadhania" <>,
	KVM <>, Jiannan Ouyang <>,
	chegu vinod <>,
	"Andrew M. Theurer" <>,
	LKML <>,
	Srivatsa Vaddagiri <>,
	Gleb Natapov <>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler

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..

> 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.

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