linux-kernel - Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw

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Message-ID: <4D501D43.5060608@redhat.com>
Date:	Mon, 07 Feb 2011 18:26:43 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
CC:	Zachary Amsden <zamsden@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	kvm <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock

On 02/07/2011 05:58 PM, Jan Kiszka wrote:
> On 2011-02-07 16:52, Avi Kivity wrote:
> >  On 02/07/2011 05:38 PM, Jan Kiszka wrote:
> >>>
> >>>   I don't know as it is allowed to sleep, it doesn't call any sleeping
> >>>   functions to my knowledge.  What worries me in the RT case is that the
> >>>   spinlock acquired for hardware_enable might be preempted and run on
> >>>   another CPU, which obviously isn't what you want.
> >>
> >>  I see now, there are calls to raw_smp_processor_id.
> >>
> >>  I think it's best to make this a raw lock. At this chance, some
> >>  read-only users of vm_list should be rcu'ified. Will have a look.
> >
> >  vm_list is rarely used, for either read or write.  I don't see the need
> >  to rcu it.
>
> Avoid that code under this lock expands the preempt-disabled period,
> specifically under -rt, and specifically as the number of objects over
> which we loop is user-defined.

Good point; even under non-rt.

(well, actually, cpufreq_notifier and kvm_arch_hardware_enable are 
already non preemptible, and the stats code should just go away?)

-- 
error compiling committee.c: too many arguments to function

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