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

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Message-ID: <4D501698.1000507@siemens.com>
Date:	Mon, 07 Feb 2011 16:58:16 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Avi Kivity <avi@...hat.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 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.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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