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Message-ID: <1348665971.3881.102.camel@twins>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler
From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Jones <drjones@redhat.com>
Cc: Avi Kivity <avi@redhat.com>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
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        KVM <kvm@vger.kernel.org>, Jiannan Ouyang <ouyang@cs.pitt.edu>,
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        "Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
        Gleb Natapov <gleb@redhat.com>
Date: Wed, 26 Sep 2012 15:26:11 +0200
In-Reply-To: <20120926132013.GB7633@turtle.usersys.redhat.com>
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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.