On 09/20/2012 10:51 AM, liu ping fan wrote:
> On Wed, Sep 19, 2012 at 5:23 PM, Avi Kivity <[email protected]> wrote:
>> On 09/19/2012 12:19 PM, liu ping fan wrote:
>>> On Wed, Sep 19, 2012 at 5:14 PM, Paolo Bonzini <[email protected]> wrote:
>>>> Il 19/09/2012 11:11, liu ping fan ha scritto:
>>>>>> > Why not? devA will drop its local lock, devX will retake the big lock
>>>>>> > recursively, devB will take its local lock. In the end, we have
>>>>>> > biglock
>>>>>> > -> devB.
>>>>>> >
>>>>> But when adopting local lock, we assume take local lock, then biglock.
>>>>
>>>> No, because the local lock will be dropped before taking the biglock.
>>>> The order must always be coarse->fine.
>>>>
>>> But if we takes coarse firstly, then the mmio-dispatcher will still
>>> contend for the big lock against each other.
>>
>> Can you detail the sequence?
>>
> LOCK(local lock)
> .......................
> LOCK(big lock)
> Access timer/block/network subsystem
> UNLOCK(big lock)
> .....................
> UNLOCK(local lock)
This is an invalid sequence. Either the subsystem has to be fine-grain
locked, or the lock order has to be reversed.
Before we finish subsystem conversion, an mmio dispatcher may look like:
dev_write(...)
{
lock(s->lock)
switch (addr) {
case REGA:
...
case REGB:
...
case REGC:
unlock(s->lock)
lock(big lock)
lock(s->lock)
qemu_mod_timer()
unlock(bit lock)
break;
...
}
unlock(s->lock)
}
--
error compiling committee.c: too many arguments to function
