On Wed, Aug 12, 2009 at 12:22:34PM +0300, Avi Kivity wrote:
> On 08/12/2009 12:11 PM, Gleb Natapov wrote:
>> On Wed, Aug 12, 2009 at 11:29:00AM +0300, Avi Kivity wrote:
>>
>>> On 08/11/2009 03:31 PM, Gleb Natapov wrote:
>>>
>>>> Change irq_lock from mutex to spinlock. We do not sleep while holding
>>>> it.
>>>>
>>>>
>>> But why change?
>>>
>>>
>> Isn't it more lightweight? For the remaining use of the lock it doesn't
>> really matters, but if I see mutex used somewhere I assume there are
>> users that sleeps.
>>
>
> Before the recent change, a mutex was more expensive if there was
> contention (waiter would schedule out). Recently the mutex code was
> changed to spin while the holder was running.
>
>>> The only motivation I can see is to allow injection from irqfd and
>>> interrupt contexts without requiring a tasklet/work. But that needs
>>> spin_lock_irqsave(), not spin_lock().
>>>
>>>
>> After this series the lock is used only to protect modification of irq
>> table, add/delete of ack notifiers and irq source id allocator. None of
>> this affects injection from irqfd.
>>
>>
>
> Then it can be definitely left as mutex.
>
OK.
--
Gleb.
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