[ovs-dev] [PATCH v2] dpif-netdev: fix race for queues between pmd threads

[Daniele Di Proietto]

Thanks for the updated patch.

One comment below

On 27/07/2015 13:19, "Ilya Maximets" <i.maximets at samsung.com> wrote:

>Currently pmd threads select queues in pmd_load_queues() according to
>get_n_pmd_threads_on_numa(). This behavior leads to race between pmds,
>beacause dp_netdev_set_pmds_on_numa() starts them one by one and
>current number of threads changes incrementally.
>
>As a result we may have the following situation with 2 pmd threads:
>
>* dp_netdev_set_pmds_on_numa()
>* pmd12 thread started. Currently only 1 pmd thread exists.
>dpif_netdev(pmd12)|INFO|Core 1 processing port 'port_1'
>dpif_netdev(pmd12)|INFO|Core 1 processing port 'port_2'
>* pmd14 thread started. 2 pmd threads exists.
>dpif_netdev|INFO|Created 2 pmd threads on numa node 0
>dpif_netdev(pmd14)|INFO|Core 2 processing port 'port_2'
>
>We have:
>core 1 --> port 1, port 2
>core 2 --> port 2
>
>Fix this by starting pmd threads only after all of them have
>been configured.
>
>Cc: Daniele Di Proietto <diproiettod at vmware.com>
>Cc: Dyasly Sergey <s.dyasly at samsung.com>
>Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
>---
> lib/dpif-netdev.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
>diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
>index 79c4612..4fca7b7 100644
>--- a/lib/dpif-netdev.c
>+++ b/lib/dpif-netdev.c
>@@ -1123,10 +1123,9 @@ do_add_port(struct dp_netdev *dp, const char
>*devname, const char *type,
>     ovs_refcount_init(&port->ref_cnt);
>     cmap_insert(&dp->ports, &port->node, hash_port_no(port_no));
> 
>-    if (netdev_is_pmd(netdev)) {
>+    if (netdev_is_pmd(netdev))
>         dp_netdev_set_pmds_on_numa(dp, netdev_get_numa_id(netdev));
>-        dp_netdev_reload_pmds(dp);
>-    }
>+

I think we should still call 'dp_netdev_reload_pmds()' when adding a
new port.

>     seq_change(dp->port_seq);
> 
>     return 0;
>@@ -2961,6 +2960,7 @@ dp_netdev_set_pmds_on_numa(struct dp_netdev *dp,
>int numa_id)
>      * pmd threads for the numa node. */
>     if (!n_pmds) {
>         int can_have, n_unpinned, i;
>+        struct dp_netdev_pmd_thread **pmds;
> 
>         n_unpinned = ovs_numa_get_n_unpinned_cores_on_numa(numa_id);
>         if (!n_unpinned) {
>@@ -2972,15 +2972,22 @@ dp_netdev_set_pmds_on_numa(struct dp_netdev *dp,
>int numa_id)
>         /* If cpu mask is specified, uses all unpinned cores, otherwise
>          * tries creating NR_PMD_THREADS pmd threads. */
>         can_have = dp->pmd_cmask ? n_unpinned : MIN(n_unpinned,
>NR_PMD_THREADS);
>+        pmds = xzalloc(can_have * sizeof *pmds);
>         for (i = 0; i < can_have; i++) {
>-            struct dp_netdev_pmd_thread *pmd = xzalloc(sizeof *pmd);
>             unsigned core_id =
>ovs_numa_get_unpinned_core_on_numa(numa_id);
>-
>-            dp_netdev_configure_pmd(pmd, dp, i, core_id, numa_id);
>+            pmds[i] = xzalloc(sizeof **pmds);
>+            dp_netdev_configure_pmd(pmds[i], dp, i, core_id, numa_id);
>+        }
>+        /* The pmd thread code needs to see all the others configured pmd
>+         * threads on the same numa node.  That's why we call
>+         * 'dp_netdev_configure_pmd()' on all the threads and then we
>actually
>+         * start them. */
>+        for (i = 0; i < can_have; i++) {
>             /* Each thread will distribute all devices rx-queues among
>              * themselves. */
>-            pmd->thread = ovs_thread_create("pmd", pmd_thread_main, pmd);
>+            pmds[i]->thread = ovs_thread_create("pmd", pmd_thread_main,
>pmds[i]);
>         }
>+        free(pmds);
>         VLOG_INFO("Created %d pmd threads on numa node %d", can_have,
>numa_id);
>     }
> }
>-- 
>2.1.4
>