On 5/23/2019 3:23 PM, David Marchand wrote:
When swapping queues from a pmd thread to another (q0 polled by pmd0/q1
polled by pmd1 -> q1 polled by pmd0/q0 polled by pmd1), the current
"Step 5" puts both pmds to sleep waiting for the control thread to wake
them up later.
Prefer to make them spin in such a case to avoid sleeping an
undeterministic amount of time.
Signed-off-by: David Marchand <david.march...@redhat.com>
Acked-by: Eelco Chaudron <echau...@redhat.com>
---
lib/dpif-netdev.c | 47 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 42 insertions(+), 5 deletions(-)
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 23cf6a6..243c1ce 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -683,6 +683,7 @@ struct dp_netdev_pmd_thread {
struct seq *reload_seq;
uint64_t last_reload_seq;
atomic_bool reload; /* Do we need to reload ports? */
+ atomic_bool wait_for_reload; /* Can we busy wait for the next reload? */
atomic_bool exit; /* For terminating the pmd thread. */
pthread_t thread;
unsigned core_id; /* CPU core id of this pmd thread. */
@@ -4896,6 +4897,33 @@ reconfigure_datapath(struct dp_netdev *dp)
HMAP_FOR_EACH_SAFE (poll, poll_next, node, &pmd->poll_list) {
if (poll->rxq->pmd != pmd) {
dp_netdev_del_rxq_from_pmd(pmd, poll);
I'm a little confused by the block below.
+
+ /* This pmd might sleep after this step reload if it has no
+ * rxq remaining. Can we tell it to busy wait for new rxq at
+ * Step 6 ? */
So whats the typical cases we target here, I would think this would
occur if PMDs have been isolated and there are no non isolated queues
available for the rxq to be assigned to?
+ if (hmap_count(&pmd->poll_list) == 0) {
+ HMAP_FOR_EACH (port, node, &dp->ports) {
+ int qid;
+
+ if (!netdev_is_pmd(port->netdev)) {
+ continue;
+ }
+
+ for (qid = 0; qid < port->n_rxq; qid++) {
+ struct dp_netdev_rxq *q = &port->rxqs[qid];
+
+ if (q->pmd == pmd) {
+ atomic_store_relaxed(&q->pmd->wait_for_reload,
+ true);
I was a little confused here, are we marking wait_for_reload true here
so that reload in step 6 will handle any new assignment? Does this not
put it in the busy-wait state already here in step 5? It's just from
reading the comment it looked like busy wait status was expected in step
6 rather than here.
Ian
+ break;
+ }
+ }
+
+ if (qid != port->n_rxq) {
+ break;
+ }
+ }
+ }
}
}
ovs_mutex_unlock(&pmd->port_mutex);
@@ -5413,7 +5441,9 @@ pmd_thread_main(void *f_)
struct pmd_perf_stats *s = &pmd->perf_stats;
unsigned int lc = 0;
struct polled_queue *poll_list;
+ bool wait_for_reload = false;
bool exiting;
+ bool reload;
int poll_cnt;
int i;
int process_packets = 0;
@@ -5441,9 +5471,16 @@ reload:
}
if (!poll_cnt) {
- while (seq_read(pmd->reload_seq) == pmd->last_reload_seq) {
- seq_wait(pmd->reload_seq, pmd->last_reload_seq);
- poll_block();
+ /* Don't sleep, control thread will ask for a reload shortly. */
+ if (wait_for_reload) {
+ do {
+ atomic_read_relaxed(&pmd->reload, &reload);
+ } while (!reload);
+ } else {
+ while (seq_read(pmd->reload_seq) == pmd->last_reload_seq) {
+ seq_wait(pmd->reload_seq, pmd->last_reload_seq);
+ poll_block();
+ }
}
lc = UINT_MAX;
}
@@ -5482,8 +5519,6 @@ reload:
}
if (lc++ > 1024) {
- bool reload;
-
lc = 0;
coverage_try_clear();
@@ -5503,6 +5538,7 @@ reload:
ovs_mutex_unlock(&pmd->perf_stats.stats_mutex);
poll_cnt = pmd_load_queues_and_ports(pmd, &poll_list);
+ atomic_read_relaxed(&pmd->wait_for_reload, &wait_for_reload);
atomic_read_relaxed(&pmd->exit, &exiting);
/* Signal here to make sure the pmd finishes
* reloading the updated configuration. */
@@ -5839,6 +5875,7 @@ dp_netdev_pmd_reload_done(struct dp_netdev_pmd_thread
*pmd)
{
uint32_t old;
+ atomic_store_relaxed(&pmd->wait_for_reload, false);
atomic_store_relaxed(&pmd->reload, false);
pmd->last_reload_seq = seq_read(pmd->reload_seq);
atomic_sub_explicit(&pmd->dp->reloading_pmds, 1, &old,
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