Re: [dpdk-dev] [PATCH v1] event/sw: performance improvements

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

<snip>

Add minimum burst throughout the scheduler pipeline and a flush counter.
Replace ring API calls with local single threaded implementation where
possible.

Signed-off-by: Radu Nicolau mailto:radu.nicolau@intel.com

Thanks for the patch, a few comments inline.

---
 drivers/event/sw/sw_evdev.h           | 11 +++-
 drivers/event/sw/sw_evdev_scheduler.c | 83
+++++++++++++++++++++++----
 2 files changed, 81 insertions(+), 13 deletions(-)

diff --git a/drivers/event/sw/sw_evdev.h b/drivers/event/sw/sw_evdev.h
index 7c77b2495..95e51065f 100644
--- a/drivers/event/sw/sw_evdev.h
+++ b/drivers/event/sw/sw_evdev.h
@@ -29,7 +29,13 @@
 /* report dequeue burst sizes in buckets */  #define
SW_DEQ_STAT_BUCKET_SHIFT 2
 /* how many packets pulled from port by sched */ -#define
SCHED_DEQUEUE_BURST_SIZE 32
+#define SCHED_DEQUEUE_BURST_SIZE 64
+
+#define SCHED_MIN_BURST_SIZE 8
+#define SCHED_NO_ENQ_CYCLE_FLUSH 256
+/* set SCHED_DEQUEUE_BURST_SIZE to 64 or 128 when setting this to 1*/
+#define SCHED_REFILL_ONCE_PER_CALL 1

Is it possible to make the above #define a runtime option?
Eg, --vdev event_sw,refill_iter=1

That would allow packaged versions of DPDK to be usable in both modes.

+

 #define SW_PORT_HIST_LIST (MAX_SW_PROD_Q_DEPTH) /* size of our
history list */  #define NUM_SAMPLES 64 /* how many data points use
for average stats */ @@ -214,6 +220,9 @@ struct sw_evdev {
     uint32_t xstats_count_mode_port;
     uint32_t xstats_count_mode_queue;

+    uint16_t sched_flush_count;
+    uint16_t sched_min_burst;
+
     /* Contains all ports - load balanced and directed */
     struct sw_port ports[SW_PORTS_MAX] __rte_cache_aligned;

diff --git a/drivers/event/sw/sw_evdev_scheduler.c
b/drivers/event/sw/sw_evdev_scheduler.c
index cff747da8..ca6d1caff 100644
--- a/drivers/event/sw/sw_evdev_scheduler.c
+++ b/drivers/event/sw/sw_evdev_scheduler.c
@@ -26,6 +26,29 @@
 /* use cheap bit mixing, we only need to lose a few bits */  #define
SW_HASH_FLOWID(f) (((f) ^ (f >> 10)) & FLOWID_MASK)

+
+/* single object enq and deq for non MT ring */ static
+__rte_always_inline void sw_nonmt_ring_dequeue(struct rte_ring *r,
+void **obj) {
+    if ((r->prod.tail - r->cons.tail) < 1)
+            return;
+    void **ring = (void **)&r[1];
+    *obj = ring[r->cons.tail & r->mask];
+    r->cons.tail++;
+}
+static __rte_always_inline int
+sw_nonmt_ring_enqueue(struct rte_ring *r, void *obj) {
+    if ((r->capacity + r->cons.tail - r->prod.tail) < 1)
+            return 0;
+    void **ring = (void **)&r[1];
+    ring[r->prod.tail & r->mask] = obj;
+    r->prod.tail++;
+    return 1;
+
Why not make these APIs part of the rte_ring library? You could further optimize them by keeping the indices on the same cacheline.
I'm not sure there is any need for non thread-safe rings outside this particular case.
[Honnappa] I think if we add the APIs, we will find the use cases.
But, more than that, I understand that rte_ring structure is exposed to the application. The reason for doing that is the inline functions that rte_ring provides. IMO, we should still maintain modularity and should not use the internals of the rte_ring structure outside of the library.

+1 to that.

BTW, is there any real perf benefit from such micor-optimisation?