On Tue, Feb 13, 2018 at 8:32 PM, Ben Pfaff <b...@ovn.org> wrote: > On Tue, Feb 13, 2018 at 12:39:56PM +0100, Daniel Alvarez Sanchez wrote: > > Hi folks, > > > > As we're doing some performance tests in OpenStack using OVN, > > we noticed that as we keep creating ports, the time for creating a > > single port increases. Also, ovn-northd CPU consumption is quite > > high (see  which shows the CPU consumption when creating > > 1000 ports and deleting them. Last part where CPU is at 100% is > > when all the ports get deleted). > > > > With 500 ports in the same Logical Switch, I did some profiling > > of OpenStack neutron-server adding 10 more ports to that Logical > > Switch. Currently, neutron-server spawns different API workers > > (separate processes) which open connections to OVN NB so every > > time an update message is sent from ovsdb-server it'll be processed > > by all of them. > > > > In my profiling, I used GreenletProfiler in all those processes to > produce > > a trace file and then merged all of them together to aggregate the > > results. In those tests I used OVS master branch compiled it with > > shared libraries to make use of the JSON C parser. Still, I've seen > > that most of the time's been spent in the following two modules: > > > > - python/ovs/db/data.py: 33% > > - uuid.py: 21% > > > > For the data.py module, this is the usage (self time): > > > > Atom.__lt__ 16.25% 8283 calls > > from_json:118 6.18% 406935 calls > > Atom.__hash__ 3.48% 1623832 calls > > from_json:328 2.01% 5040 calls > > > > While for the uuid module: > > > > UUID.__cmp__ 12.84% 3570975 calls > > UUID.__init__ 4.06% 362541 calls > > UUID.__hash__ 2.96% 1800 calls > > UUID.__str__ 1.03% 355016 calls > > > > Most of the calls to Atom.__lt__ come from > > BaseOvnIdl.__process_update2(idl.py) > > -> BaseOvnIdl.__row_update(idl.py) -> Datum.__cmp__(data.py) -> > > Atom.__cmp__(data.py). > > I don't know Python well enough to whether these are "real" or correct > optimizations, but the following strike me as possible low-hanging fruit > micro-optimizations: > > diff --git a/python/ovs/db/data.py b/python/ovs/db/data.py > index 9e57595f7513..dc816f64708f 100644 > --- a/python/ovs/db/data.py > +++ b/python/ovs/db/data.py > @@ -76,12 +76,12 @@ class Atom(object): > def __eq__(self, other): > if not isinstance(other, Atom) or self.type != other.type: > return NotImplemented > - return True if self.value == other.value else False > + return self.value == other.value > > def __lt__(self, other): > if not isinstance(other, Atom) or self.type != other.type: > return NotImplemented > - return True if self.value < other.value else False > + return self.value < other.value > > def __cmp__(self, other): > if not isinstance(other, Atom) or self.type != other.type: > > We could also reduce the number of calls to Datum.__cmp__ by recognizing > that if we've already found one change we don't have to do any more > comparisons, something like this: > > diff --git a/python/ovs/db/idl.py b/python/ovs/db/idl.py > index 60548bcf50b6..2e550adfdf1c 100644 > --- a/python/ovs/db/idl.py > +++ b/python/ovs/db/idl.py > @@ -447,6 +447,7 @@ class Idl(object): > raise error.Error("<table-updates> is not an object", > table_updates) > > + changed = False > for table_name, table_update in six.iteritems(table_updates): > table = self.tables.get(table_name) > if not table: > @@ -472,8 +473,8 @@ class Idl(object): > % (table_name, uuid_string)) > > if version == OVSDB_UPDATE2: > - if self.__process_update2(table, uuid, row_update): > - self.change_seqno += 1 > + changed = self.__process_update2(table, uuid, > row_update, > + changed) > continue > > parser = ovs.db.parser.Parser(row_update, "row-update") > @@ -485,12 +486,12 @@ class Idl(object): > raise error.Error('<row-update> missing "old" and ' > '"new" members', row_update) > > - if self.__process_update(table, uuid, old, new): > - self.change_seqno += 1 > + changed = self.__process_update(table, uuid, old, new, > changed) > + if changed: > + self.change_seqno += 1 > > - def __process_update2(self, table, uuid, row_update): > + def __process_update2(self, table, uuid, row_update, changed): > row = table.rows.get(uuid) > - changed = False > if "delete" in row_update: > if row: > del table.rows[uuid] > @@ -511,9 +512,8 @@ class Idl(object): > else: > row_update = row_update['initial'] > self.__add_default(table, row_update) > - if self.__row_update(table, row, row_update): > - changed = True > - self.notify(ROW_CREATE, row) > + changed = self.__row_update(table, row, row_update, changed) > + self.notify(ROW_CREATE, row) > elif "modify" in row_update: > if not row: > raise error.Error('Modify non-existing row') > @@ -528,10 +528,9 @@ class Idl(object): > row_update) > return changed > > - def __process_update(self, table, uuid, old, new): > + def __process_update(self, table, uuid, old, new, changed): > """Returns True if a column changed, False otherwise.""" > row = table.rows.get(uuid) > - changed = False > if not new: > # Delete row. > if row: > @@ -547,13 +546,13 @@ class Idl(object): > if not row: > row = self.__create_row(table, uuid) > changed = True > + self.__row_update(table, row, new, True) > + self.notify(ROW_CREATE, row) > else: > # XXX rate-limit > vlog.warn("cannot add existing row %s to table %s" > % (uuid, table.name)) > - if self.__row_update(table, row, new): > - changed = True > - self.notify(ROW_CREATE, row) > + changed = self.__row_update(table, row, new, changed) > else: > op = ROW_UPDATE > if not row: > @@ -563,9 +562,8 @@ class Idl(object): > # XXX rate-limit > vlog.warn("cannot modify missing row %s in table %s" > % (uuid, table.name)) > - if self.__row_update(table, row, new): > - changed = True > - self.notify(op, row, Row.from_json(self, table, uuid, > old)) > + changed = self.__row_update(table, row, new, changed) > + self.notify(op, row, Row.from_json(self, table, uuid, old)) > return changed > > def __column_name(self, column): > @@ -608,8 +606,7 @@ class Idl(object): > > return old_row_diff_json > > - def __row_update(self, table, row, row_json): > - changed = False > + def __row_update(self, table, row, row_json, changed): > for column_name, datum_json in six.iteritems(row_json): > column = table.columns.get(column_name) > if not column: > @@ -626,14 +623,13 @@ class Idl(object): > % (column_name, table.name, e)) > continue > > - if datum != row._data[column_name]: > + # If the column changed, update it and record that we saw a > change. > + # We also update it if we've already recorded some other > change, > + # because that's cheaper than doing an unnecessary comparison. > + if changed or datum != row._data[column_name]: > row._data[column_name] = datum > if column.alert: > changed = True > - else: > - # Didn't really change but the OVSDB monitor protocol > always > - # includes every value in a row. > - pass > return changed > > def __create_row(self, table, uuid): > > FWIW, I have tried this patch on the same scenario of the whole thread and there's no gain. However I think the optimizations make sense and once we have the Port sets, they're going to be more noticeable.
> > The aggregated number of calls to BaseOvnIdl.__process_update2 is > > 1400 (and we're updating only 10 ports!!) while the total connections > > opened to NB database are 10: > > > > # netstat -np | grep 6641 | grep python | wc -l > > 10 > > > > * Bear in mind that those results above were aggregated across all > > processes. > > > > Looks like the main culprit for this explosion could be the way we > > handle ACLs. As every time we create a port, it'll belong to a Neutron > > security group (OVN Address Set) and we'll add a new ACL for every > > Neutron security group rule. If we patch the code to skip the ACL part, > > the time for creating a port remains stable over the time. > > > > From the comparison tests against ML2/OVS (reference implementation), > > OVN outperforms in most of the operations except for the port creation > > where we can see it can become a bottleneck. > > > > Before optimizing/redesigning the ACL part, we could do some other > > changes to the way we handle notifications from OVSDB: eg., instead of > > having multiple processes receiving *all* notifications, we could have > > one single process subscribed to those notifications and send a more > > optimized (already parsed) multicast notification to all listening > processes > > to keep their own in-memory copies of the DB up to date. All processes > > would connect to NB database in "write-only" mode to commit their > > transactions however. > > I'm not sure I understand this. What information is it unnecessary to > have the processes receive? If they are getting information they don't > need, then we might be able to eliminate some of it. > > Can you sketch the rows that are being inserted or modified when a port > is added? I would expect something like this as a minimum: > > * Insert one Logical_Switch_Port row. > > * Add pointer to Logical_Switch_Port to ports column in one row > in Logical_Switch. > > In addition it sounds like currently we're seeing: > > * Add one ACL row per security group rule. > > * Add pointers to ACL rows to acls column in one row in > Logical_Switch. > > and that's the bottleneck? >
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