When ping-pong'in a live VM migration between two machines running OVS-DPDK every now and then the ping misses would increase dramatically. For example:
===========Stream Rate: 3Mpps=========== No Stream_Rate Downtime Totaltime Ping_Loss Moongen_Loss 0 3Mpps 128 13974 115 7168374 1 3Mpps 145 13620 17 1169770 2 3Mpps 140 14499 116 7141175 3 3Mpps 142 13358 16 1150606 4 3Mpps 136 14004 16 1124020 5 3Mpps 139 15494 214 13170452 6 3Mpps 136 15610 217 13282413 7 3Mpps 146 13194 17 1167512 8 3Mpps 148 12871 16 1162655 9 3Mpps 137 15615 214 13170656 I identified this issue being introduced in OVS commit https://github.com/openvswitch/ovs/commit/f3e7ec254738364101eed8f04b1d954cb510615c and more specific due to DPDK commit http://dpdk.org/browse/dpdk/commit/?id=af14759181240120f76c82f894982e8f33f0ba2a The combined changes no longer have OVS start the vhost socket polling thread at startup, but DPDK will do it on its own when the first vhost client is started. Figuring out the reason why this happens kept me puzzled for quite some time... What happens is that the callbacks called from the vhost thread are calling ovsrcu_synchronize() as part of destroy_device(). This will end-up calling seq_wait__(), and the problem is with this part: 176static void 177seq_wait__(struct seq *seq, uint64_t value, const char *where) 178 OVS_REQUIRES(seq_mutex) 179{ >> 180 unsigned int id = ovsthread_id_self(); 181 uint32_t hash = hash_int(id, 0); 182 struct seq_waiter *waiter; 183 184 HMAP_FOR_EACH_IN_BUCKET (waiter, hmap_node, hash, &seq->waiters) { >> 185 if (waiter->ovsthread_id == id) { 186 if (waiter->value != value) { 187 /* The current value is different from the value we've already 188 * waited for, */ 189 poll_immediate_wake_at(where); 190 } else { 191 /* Already waiting on 'value', nothing more to do. */ 192 } >> 193 return; 194 } 195 } 196 By default, all created threads outside of OVS will get thread id 0, which is equal to the main ovs thread. So for example in the function above if the main thread is waiting already we won't add ourselves as a waiter. The fix below assigns UINT_MAX to none OVS created threads, which will fix this specific issue. However if more none OVS threads gets added the issue might arise again. Currently, I do not see another solution that will work unless DPDK is adding some framework/callback support when new threads get created. Signed-off-by: Eelco Chaudron <echau...@redhat.com> --- lib/ovs-thread.c | 2 +- lib/ovs-thread.h | 7 +++++++ vswitchd/ovs-vswitchd.c | 2 ++ 3 files changed, 10 insertions(+), 1 deletion(-) diff --git a/lib/ovs-thread.c b/lib/ovs-thread.c index f8bc06d38..e663794ea 100644 --- a/lib/ovs-thread.c +++ b/lib/ovs-thread.c @@ -315,7 +315,7 @@ ovs_barrier_block(struct ovs_barrier *barrier) } } -DEFINE_EXTERN_PER_THREAD_DATA(ovsthread_id, 0); +DEFINE_EXTERN_PER_THREAD_DATA(ovsthread_id, UINT_MAX); struct ovsthread_aux { void *(*start)(void *); diff --git a/lib/ovs-thread.h b/lib/ovs-thread.h index 03fd80439..4f543eb57 100644 --- a/lib/ovs-thread.h +++ b/lib/ovs-thread.h @@ -525,4 +525,11 @@ bool may_fork(void); int count_cpu_cores(void); bool thread_is_pmd(void); +static inline void +ovsthread_set_id(unsigned int id) +{ + assert_single_threaded(); + *ovsthread_id_get() = id; +} + #endif /* ovs-thread.h */ diff --git a/vswitchd/ovs-vswitchd.c b/vswitchd/ovs-vswitchd.c index 414b54780..ed456e2d2 100644 --- a/vswitchd/ovs-vswitchd.c +++ b/vswitchd/ovs-vswitchd.c @@ -39,6 +39,7 @@ #include "ovsdb-idl.h" #include "ovs-rcu.h" #include "ovs-router.h" +#include "ovs-thread.h" #include "openvswitch/poll-loop.h" #include "simap.h" #include "stream-ssl.h" @@ -78,6 +79,7 @@ main(int argc, char *argv[]) int retval; set_program_name(argv[0]); + ovsthread_set_id(0); ovs_cmdl_proctitle_init(argc, argv); service_start(&argc, &argv); -- 2.17.0 _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev
