[ovs-dev] [PATCH 2/7] ofproto: Lock for vlan splinters only if have them.

Jarno Rajahalme jrajahalme at nicira.com
Wed Feb 12 16:59:18 UTC 2014


On Feb 11, 2014, at 4:40 PM, Ben Pfaff <blp at nicira.com> wrote:

> On Tue, Feb 11, 2014 at 04:30:44PM -0800, Jarno Rajahalme wrote:
>> Reading the hmap count for determining if it is empty or not is thread
>> safe, so avoid locking when not necessary.
>> 
>> Signed-off-by: Jarno Rajahalme <jrajahalme at nicira.com>
> 
> It might be worth adding an atomic_thread_fence(memory_order_acquire);
> before the hmap_is_empty() checks, so that we can be sure to get "fresh"
> results in case that some other CPU has modified the hmap.  (On x86,
> with GCC 4.7, this generates no code.)

Would this be best placed in the hmap_is_empty() itself?

  Jarno




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