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SubjectRe: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock
On 2011-02-07 17:26, Avi Kivity wrote:
> 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?)

The stats code is trivial to convert, so it doesn't matter.

But what about mmu_shrink and its list_move_tail? How is this
synchronized against kvm_destroy_vm - already today?

Jan

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


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