On 29 August 2015 at 15:24, Alex Wang <al...@nicira.com> wrote:
>
>
> On Sat, Aug 29, 2015 at 11:34 AM, Joe Stringer <joestrin...@nicira.com>
> wrote:
>>
>> Thanks for working on this, Alex. I've considered implementing an
>> approach like this before, but haven't had a strong reason to.
>>
>> On 29 August 2015 at 00:42, Alex Wang <ee07b...@gmail.com> wrote:
>> > This commit adds logic using ovs barrier to allow main thread pause
>> > all revalidators. This new feature will be used in a later patch.
>> >
>> > Signed-off-by: Alex Wang <ee07b...@gmail.com>
>>
>> <snip>
>>
>> > @@ -762,6 +791,11 @@ udpif_revalidator(void *arg)
>> >
>> > revalidator->id = ovsthread_id_self();
>> > for (;;) {
>> > + /* Pauses all revalidators if wanted. */
>> > + if (latch_is_set(&udpif->pause_latch)) {
>> > + revalidator_pause(revalidator);
>> > + }
>> > +
>>
>> Is there anything that ensures all revalidators are either before this
>> statement, or after this statement, when the latch is modified?
>
>
> I think this should not matter, since the latch_wait() will cause
> revalidator
> waking up immediately... And latch has only two states (set or not), unlike
> the sequence number, so we do not need to worry about missing the
> seq_change,
What if the threads don't wake up due to latch_wait(), but due to
another reason? Each revalidator thread individually checks the value
at a different time from all the others, so without a critical section
that ensures they all check the same value, I think it's possible for
two revalidators to wake up (eg due to timer expiring), one checks the
latch & skips the barrier, then main thread changes the latch, then
the second revalidator checks the latch & blocks on the barrier.
_______________________________________________
dev mailing list
dev@openvswitch.org
http://openvswitch.org/mailman/listinfo/dev
