On 30.04.2019 15:17, David Marchand wrote:
> No need for a latch here since we don't have to wait.
> A simple boolean flag is enough.
>
> Fixes: e4cfed38b159 ("dpif-netdev: Add poll-mode-device thread.")
> Signed-off-by: David Marchand <david.march...@redhat.com>
> ---
> lib/dpif-netdev.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index f1422b2..30774ed 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -681,10 +681,10 @@ struct dp_netdev_pmd_thread {
> /* Current context of the PMD thread. */
> struct dp_netdev_pmd_thread_ctx ctx;
>
> - struct latch exit_latch; /* For terminating the pmd thread. */
> struct seq *reload_seq;
> uint64_t last_reload_seq;
> atomic_bool reload; /* Do we need to reload ports? */
> + atomic_bool exit; /* For terminating the pmd thread. */
> pthread_t thread;
> unsigned core_id; /* CPU core id of this pmd thread. */
> int numa_id; /* numa node id of this pmd thread. */
> @@ -5479,7 +5479,7 @@ reload:
> ovs_mutex_unlock(&pmd->perf_stats.stats_mutex);
>
> poll_cnt = pmd_load_queues_and_ports(pmd, &poll_list);
> - exiting = latch_is_set(&pmd->exit_latch);
> + atomic_read_relaxed(&pmd->exit, &exiting);
I'm afraid that relaxed memory model is not suitable here.
You need to change memory models for both 'reload' and 'exit'
or put ack_rel thread fence between them. Otherwise reads/writes
could be reordered resulting in missed exit and main thread
hang on join.
> /* Signal here to make sure the pmd finishes
> * reloading the updated configuration. */
> dp_netdev_pmd_reload_done(pmd);
> @@ -5898,7 +5898,7 @@ dp_netdev_configure_pmd(struct dp_netdev_pmd_thread
> *pmd, struct dp_netdev *dp,
> pmd->n_output_batches = 0;
>
> ovs_refcount_init(&pmd->ref_cnt);
> - latch_init(&pmd->exit_latch);
> + atomic_init(&pmd->exit, false);
> pmd->reload_seq = seq_create();
> pmd->last_reload_seq = seq_read(pmd->reload_seq);
> atomic_init(&pmd->reload, false);
> @@ -5945,7 +5945,6 @@ dp_netdev_destroy_pmd(struct dp_netdev_pmd_thread *pmd)
> cmap_destroy(&pmd->classifiers);
> cmap_destroy(&pmd->flow_table);
> ovs_mutex_destroy(&pmd->flow_mutex);
> - latch_destroy(&pmd->exit_latch);
> seq_destroy(pmd->reload_seq);
> xpthread_cond_destroy(&pmd->cond);
> ovs_mutex_destroy(&pmd->cond_mutex);
> @@ -5967,7 +5966,7 @@ dp_netdev_del_pmd(struct dp_netdev *dp, struct
> dp_netdev_pmd_thread *pmd)
> pmd_free_static_tx_qid(pmd);
> ovs_mutex_unlock(&dp->non_pmd_mutex);
> } else {
> - latch_set(&pmd->exit_latch);
> + atomic_store_relaxed(&pmd->exit, true);
> dp_netdev_reload_pmd__(pmd);
> xpthread_join(pmd->thread, NULL);
> }
>
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