On Jun 2, 2014, at 11:45 AM, Ben Pfaff <b...@nicira.com> wrote:
> I'd really hope that any serious OVS implementation would be able to
> use C11 or GCC or Clang or other compiler-specific techniques to get a
> "real" implementation of atomics. Really the pthreads version is just
> to make porting easier.
>
Are we already documenting this somewhere?
Jarno
> On Mon, Jun 02, 2014 at 11:07:12AM -0700, Jarno Rajahalme wrote:
>> As I?m testing for this I notice that the cmap (or, ovs-rcu) with
>> ova-atomic-pthreads is painfully slow. The reason for this is the
>> the generic pthreads atomics have no memory barrier support, which
>> is needed for efficient RCU. As we make more use of ovs-rcu and cmap
>> we need to address this in one way or another. it may even become
>> necessary to deprecate support for systems for which we have no
>> memory barriers.
>>
>> Thoughts?
>>
>> Jarno
>>
>> On Jun 2, 2014, at 10:43 AM, Jarno Rajahalme <jrajaha...@nicira.com> wrote:
>>
>>> Thanks for reporting this!
>>>
>>> I think we should allow the illusion that ovsrcu_init is a function, and
>>> it?s parameters are evaluated before the body. Otherwise problems like this
>>> are bound to be reintroduced. I?ll post a patch soon.
>>>
>>> Jarno
>>>
>>> On Jun 2, 2014, at 3:34 AM, YAMAMOTO Takashi <yamam...@valinux.co.jp> wrote:
>>>
>>>> In the case of ovs-atomic-pthreads, the previous coding is expanded
>>>> into successive atomic_lock__ calls which ends up with deadlock.
>>>>
>>>> Signed-off-by: YAMAMOTO Takashi <yamam...@valinux.co.jp>
>>>> ---
>>>> lib/cmap.c | 4 +++-
>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/cmap.c b/lib/cmap.c
>>>> index a760235..7892d50 100644
>>>> --- a/lib/cmap.c
>>>> +++ b/lib/cmap.c
>>>> @@ -690,7 +690,9 @@ cmap_replace__(struct cmap_impl *impl, struct
>>>> cmap_node *node,
>>>> replacement = cmap_node_next_protected(node);
>>>> } else {
>>>> /* 'replacement' takes the position of 'node' in the list. */
>>>> - ovsrcu_init(&replacement->next, cmap_node_next_protected(node));
>>>> + struct cmap_node *next = cmap_node_next_protected(node);
>>>> +
>>>> + ovsrcu_init(&replacement->next, next);
>>>> }
>>>>
>>>> struct cmap_node *iter = &b->nodes[slot];
>>>> --
>>>> 1.8.3.1
>>>>
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>>>
>>
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