[ovs-dev] [PATCH] ovn-controller: Fix flow installation latency caused by recompute.

Han Zhou zhouhan at gmail.com
Tue Jul 30 07:16:56 UTC 2019


Thanks Mark and Numan for the review.
Ben, now this is merged to OVN repo. Could you help backporting it to 2.12?

Thanks,
Han


On Thu, Jul 25, 2019 at 1:23 PM Mark Michelson <mmichels at redhat.com> wrote:
>
> Forgot the e-mail address after my name :)
>
> Acked-by: Mark Michelson <mmichels at redhat.com>
>
> On 7/25/19 4:16 PM, Mark Michelson wrote:
> > Acked-by: Mark Michelson
> >
> > Thanks for the informative commit message!
> >
> > On 7/23/19 10:52 PM, Han Zhou wrote:
> >> From: Han Zhou <hzhou8 at ebay.com>
> >>
> >> When there are in-flight flow-installations pending to ovs-vswitchd,
> >> current incremental processing logic prioritizes new change handling.
> >> However, in scenarios where frequent recomputes are triggered, the
> >> later recompute would block the flow-installation for previously
> >> computed flows because recompute usually takes long time, especially
> >> when there are large number of flows. This results in worse latency
> >> than the version without incremental processing in specific scale
> >> test scenarios.
> >>
> >> While we can simply fix the problem by prioritizing flow installation
> >> rather than new change handling, it can cause the incremental
> >> processing to degrade to always recompute in certain scenarios when
> >> there are some changes triggering recomputes, followed by a lot of
> >> continously coming changes that can be handled incrementally. Because
> >> OVSDB change tracker cannot preserve changes across iterations, once
> >> the recompute is triggered and resulted in a lot of pending messages
> >> to ovs-vswitchd, and if we choose to skip the engine_run()
> >> in the next iteration when a incrementally processible change comes,
> >> we miss the opportunity to handle that tracked change and will have
> >> to trigger recompute again in the next next iteration, and so on, if
> >> such changes come continously.
> >>
> >> This patch solves the problem by introducing
> >> engine_set_abort_recompute(),
> >> so that we can prioritize new change handling if the change can be
> >> incrementally processed, but if the change triggers recompute, we
> >> abort there without spending CPU on the recompute to avoid blocking
> >> the previous computed flow installation.
> >>
> >> Reported-by: Daniel Alvarez Sanchez <dalvarez at redhat.com>
> >> Reported-by: Numan Siddique <nusiddiq at redhat.com>
> >> Reported-at:
> >>
https://mail.openvswitch.org/pipermail/ovs-discuss/2019-June/048822.html
> >> Tested-by: Numan Siddique <nusiddiq at redhat.com>
> >> Signed-off-by: Han Zhou <hzhou8 at ebay.com>
> >> ---
> >>   ovn/controller/ofctrl.c         |  2 +-
> >>   ovn/controller/ofctrl.h         |  1 +
> >>   ovn/controller/ovn-controller.c | 30 +++++++++++++++++++++++++++---
> >>   ovn/lib/inc-proc-eng.c          | 26 ++++++++++++++++++++++----
> >>   ovn/lib/inc-proc-eng.h          |  9 +++++++--
> >>   5 files changed, 58 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/ovn/controller/ofctrl.c b/ovn/controller/ofctrl.c
> >> index 043abd6..0fcaa72 100644
> >> --- a/ovn/controller/ofctrl.c
> >> +++ b/ovn/controller/ofctrl.c
> >> @@ -985,7 +985,7 @@ add_meter(struct ovn_extend_table_info *m_desired,
> >>    * in the correct state and not backlogged with existing flow_mods.
> >> (Our
> >>    * criteria for being backlogged appear very conservative, but the
> >> socket
> >>    * between ovn-controller and OVS provides some buffering.) */
> >> -static bool
> >> +bool
> >>   ofctrl_can_put(void)
> >>   {
> >>       if (state != S_UPDATE_FLOWS
> >> diff --git a/ovn/controller/ofctrl.h b/ovn/controller/ofctrl.h
> >> index ed8918a..2b21c11 100644
> >> --- a/ovn/controller/ofctrl.h
> >> +++ b/ovn/controller/ofctrl.h
> >> @@ -51,6 +51,7 @@ void ofctrl_put(struct ovn_desired_flow_table *,
> >>                   const struct sbrec_meter_table *,
> >>                   int64_t nb_cfg,
> >>                   bool flow_changed);
> >> +bool ofctrl_can_put(void);
> >>   void ofctrl_wait(void);
> >>   void ofctrl_destroy(void);
> >>   int64_t ofctrl_get_cur_cfg(void);
> >> diff --git a/ovn/controller/ovn-controller.c
> >> b/ovn/controller/ovn-controller.c
> >> index c4883aa..866cc1c 100644
> >> --- a/ovn/controller/ovn-controller.c
> >> +++ b/ovn/controller/ovn-controller.c
> >> @@ -1869,6 +1869,7 @@ main(int argc, char *argv[])
> >>       uint64_t engine_run_id = 0;
> >>       uint64_t old_engine_run_id = 0;
> >> +    bool engine_aborted = false;
> >>       unsigned int ovs_cond_seqno = UINT_MAX;
> >>       unsigned int ovnsb_cond_seqno = UINT_MAX;
> >> @@ -1955,7 +1956,30 @@ main(int argc, char *argv[])
> >>                       stopwatch_start(CONTROLLER_LOOP_STOPWATCH_NAME,
> >>                                       time_msec());
> >>                       if (ovnsb_idl_txn) {
> >> -                        engine_run(&en_flow_output, ++engine_run_id);
> >> +                        if (!ofctrl_can_put()) {
> >> +                            /* When there are in-flight messages
> >> pending to
> >> +                             * ovs-vswitchd, we should hold on
> >> recomputing so
> >> +                             * that the previous flow installations
> >> won't be
> >> +                             * delayed.  However, we still want to
> >> try if
> >> +                             * recompute is not needed and we can
> >> quickly
> >> +                             * incrementally process the new changes,
> >> to avoid
> >> +                             * unnecessarily forced recomputes later
> >> on.  This
> >> +                             * is because the OVSDB change tracker
> >> cannot
> >> +                             * preserve tracked changes across
> >> iterations.  If
> >> +                             * change tracking is improved, we can
> >> simply skip
> >> +                             * this round of engine_run and continue
> >> processing
> >> +                             * acculated changes incrementally later
> >> when
> >> +                             * ofctrl_can_put() returns true. */
> >> +                            if (!engine_aborted) {
> >> +                                engine_set_abort_recompute(true);
> >> +                                engine_aborted =
> >> engine_run(&en_flow_output,
> >> +
> >> ++engine_run_id);
> >> +                            }
> >> +                        } else {
> >> +                            engine_set_abort_recompute(false);
> >> +                            engine_aborted = false;
> >> +                            engine_run(&en_flow_output,
> >> ++engine_run_id);
> >> +                        }
> >>                       }
> >>                       stopwatch_stop(CONTROLLER_LOOP_STOPWATCH_NAME,
> >>                                      time_msec());
> >> @@ -1993,8 +2017,8 @@ main(int argc, char *argv[])
> >>                   }
> >>               }
> >> -            if (old_engine_run_id == engine_run_id) {
> >> -                if (engine_need_run(&en_flow_output)) {
> >> +            if (old_engine_run_id == engine_run_id || engine_aborted)
{
> >> +                if (engine_aborted ||
> >> engine_need_run(&en_flow_output)) {
> >>                       VLOG_DBG("engine did not run, force recompute
> >> next time: "
> >>                                "br_int %p, chassis %p", br_int,
chassis);
> >>                       engine_set_force_recompute(true);
> >> diff --git a/ovn/lib/inc-proc-eng.c b/ovn/lib/inc-proc-eng.c
> >> index 1ddea1a..1064a08 100644
> >> --- a/ovn/lib/inc-proc-eng.c
> >> +++ b/ovn/lib/inc-proc-eng.c
> >> @@ -31,6 +31,7 @@
> >>   VLOG_DEFINE_THIS_MODULE(inc_proc_eng);
> >>   static bool engine_force_recompute = false;
> >> +static bool engine_abort_recompute = false;
> >>   static const struct engine_context *engine_context;
> >>   void
> >> @@ -39,6 +40,12 @@ engine_set_force_recompute(bool val)
> >>       engine_force_recompute = val;
> >>   }
> >> +void
> >> +engine_set_abort_recompute(bool val)
> >> +{
> >> +    engine_abort_recompute = val;
> >> +}
> >> +
> >>   const struct engine_context *
> >>   engine_get_context(void)
> >>   {
> >> @@ -121,11 +128,11 @@ engine_ovsdb_node_add_index(struct engine_node
> >> *node, const char *name,
> >>       ed->n_indexes ++;
> >>   }
> >> -void
> >> +bool
> >>   engine_run(struct engine_node *node, uint64_t run_id)
> >>   {
> >>       if (node->run_id == run_id) {
> >> -        return;
> >> +        return true;
> >>       }
> >>       node->run_id = run_id;
> >> @@ -133,11 +140,13 @@ engine_run(struct engine_node *node, uint64_t
> >> run_id)
> >>       if (!node->n_inputs) {
> >>           node->run(node);
> >>           VLOG_DBG("node: %s, changed: %d", node->name, node->changed);
> >> -        return;
> >> +        return true;
> >>       }
> >>       for (size_t i = 0; i < node->n_inputs; i++) {
> >> -        engine_run(node->inputs[i].node, run_id);
> >> +        if (!engine_run(node->inputs[i].node, run_id)) {
> >> +            return false;
> >> +        }
> >>       }
> >>       bool need_compute = false;
> >> @@ -160,6 +169,10 @@ engine_run(struct engine_node *node, uint64_t
> >> run_id)
> >>       if (need_recompute) {
> >>           VLOG_DBG("node: %s, recompute (%s)", node->name,
> >>                    engine_force_recompute ? "forced" : "triggered");
> >> +        if (engine_abort_recompute) {
> >> +            VLOG_DBG("node: %s, recompute aborted", node->name);
> >> +            return false;
> >> +        }
> >>           node->run(node);
> >>       } else if (need_compute) {
> >>           for (size_t i = 0; i < node->n_inputs; i++) {
> >> @@ -170,6 +183,10 @@ engine_run(struct engine_node *node, uint64_t
> >> run_id)
> >>                       VLOG_DBG("node: %s, can't handle change for
> >> input %s, "
> >>                                "fall back to recompute",
> >>                                node->name, node->inputs[i].node->name);
> >> +                    if (engine_abort_recompute) {
> >> +                        VLOG_DBG("node: %s, recompute aborted",
> >> node->name);
> >> +                        return false;
> >> +                    }
> >>                       node->run(node);
> >>                       break;
> >>                   }
> >> @@ -178,6 +195,7 @@ engine_run(struct engine_node *node, uint64_t
run_id)
> >>       }
> >>       VLOG_DBG("node: %s, changed: %d", node->name, node->changed);
> >> +    return true;
> >>   }
> >>   bool
> >> diff --git a/ovn/lib/inc-proc-eng.h b/ovn/lib/inc-proc-eng.h
> >> index aab899e..c3d7b5e 100644
> >> --- a/ovn/lib/inc-proc-eng.h
> >> +++ b/ovn/lib/inc-proc-eng.h
> >> @@ -121,8 +121,9 @@ struct engine_node {
> >>   void engine_init(struct engine_node *);
> >>   /* Execute the processing recursively, which should be called in the
> >> main
> >> - * loop. */
> >> -void engine_run(struct engine_node *, uint64_t run_id);
> >> + * loop. Returns true if the execution is compelte, false if it is
> >> aborted,
> >> + * which could happen when engine_abort_recompute is set. */
> >> +bool engine_run(struct engine_node *, uint64_t run_id);
> >>   /* Clean up the data for the engine nodes recursively. It calls each
> >> node's
> >>    * cleanup() method if not NULL. It should be called before the
program
> >> @@ -150,6 +151,10 @@ void engine_add_input(struct engine_node *node,
> >> struct engine_node *input,
> >>    * iteration, and the change can't be tracked across iterations */
> >>   void engine_set_force_recompute(bool val);
> >> +/* Set the flag to cause engine execution to be aborted when there
> >> + * is any recompute to be triggered in any node. */
> >> +void engine_set_abort_recompute(bool val);
> >> +
> >>   const struct engine_context * engine_get_context(void);
> >>   void engine_set_context(const struct engine_context *);
> >>
> >
>


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