> On 11/22/2010 12:39 AM, Cypher Wu wrote:
>> 2010/11/15 Chris Metcalf <cmetcalf@tilera.com>:
>>> This avoids a deadlock in the IGMP code where one core gets a read
>>> lock, another core starts trying to get a write lock (thus blocking
>>> new readers), and then the first core tries to recursively re-acquire
>>> the read lock.
>>>
>>> We still try to preserve some degree of balance by giving priority
>>> to additional write lockers that come along while the lock is held
>>> for write, so they can all complete quickly and return the lock to
>>> the readers.
>>>
>>> Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
>>> ---
>>> This should apply relatively cleanly to 2.6.26.7 source code too.
>>> [...]
>>
>> I've finished my business trip and tested that patch for more than an
>> hour and it works. The test is still running now.
>>
>> But it seems there still has a potential problem: we used ticket lock
>> for write_lock(), and if there are so many write_lock() occurred, is
>> 256 ticket enough for 64 or even more cores to avoiding overflow?
>> Since is we try to write_unlock() and there's already write_lock()
>> waiting we'll only adding current ticket.
>
> This is OK, since each core can issue at most one (blocking) write_lock(),
> and we have only 64 cores. Future >256 core machines will be based on
> TILE-Gx anyway, which doesn't have the 256-core limit since it doesn't use
> the spinlock_32.c implementation.
>
> --
> Chris Metcalf, Tilera Corp.
>
http://www.tilera.com
>
>
