linux-kernel - Re: SMP lockup in virtualized environment

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Message-ID: <462E86BF.7010402@redhat.com>
Date:	Tue, 24 Apr 2007 18:37:51 -0400
From:	Chris Snook <csnook@...hat.com>
To:	LAPLACE Cyprien <cyprien.laplace@...ngo-systems.com>
CC:	virtualization@...ts.linux-foundation.org,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: SMP lockup in virtualized environment

LAPLACE Cyprien wrote:
> An example: in kernel/pid.c:alloc_pid(), if one of the guest CPUs is
> descheduled when holding the pidmap_lock, what happens to the other
> guest CPUs who want to alloc/free pids ? Are they blocked too ?

Yup.  This is where it's really nice to have directed yields, where you tell the 
hypervisor to give your physical CPU time to the vcpu that's holding the lock 
you're blocking on.  I know s390 can do this.  Perhaps it's something worth 
generalizing in paravirt_ops?

	-- Chris
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