[dpdk-dev] [PATCH 8/8] event/dsw: add port busy cycles xstats

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

DSW keeps an internal port load estimate, used by the load balancing
mechanism. As a side effect, it keeps track of the total number of
busy cycles since startup. This metric is indirectly exposed in the
form of DSW xstats' "port_<n>_event_proc_latency", which is the total
number of busy cycles divided by the total number of events processed
on a particular port.

An external application can take (event_latency * dequeued) to go back
to busy_cycles. One reason for doing this is to measure the port's
load during a longer time period, without resorting to sampling
"port_<n>_load". However, as the number dequeued events grows, a
rounding error in event_latency renders the application-calculated
busy_cycles inaccurate.

Thus, it makes sense to directly expose the number of busy cycles as a
DSW xstats, even though it might seem redundant.

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
---
 drivers/event/dsw/dsw_xstats.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/event/dsw/dsw_xstats.c b/drivers/event/dsw/dsw_xstats.c
index d332a57b6..e8e92183e 100644
--- a/drivers/event/dsw/dsw_xstats.c
+++ b/drivers/event/dsw/dsw_xstats.c
@@ -109,6 +109,13 @@ dsw_xstats_port_get_event_proc_latency(struct dsw_evdev *dsw, uint8_t port_id,
 	return dequeued > 0 ? total_busy_cycles / dequeued : 0;
 }
 
+static uint64_t
+dsw_xstats_port_get_busy_cycles(struct dsw_evdev *dsw, uint8_t port_id,
+				uint8_t queue_id __rte_unused)
+{
+	return dsw->ports[port_id].total_busy_cycles;
+}
+
 DSW_GEN_PORT_ACCESS_FN(inflight_credits)
 
 DSW_GEN_PORT_ACCESS_FN(pending_releases)
@@ -147,6 +154,8 @@ static struct dsw_xstats_port dsw_port_xstats[] = {
 	  false },
 	{ "port_%u_event_proc_latency", dsw_xstats_port_get_event_proc_latency,
 	  false },
+	{ "port_%u_busy_cycles", dsw_xstats_port_get_busy_cycles,
+	  false },
 	{ "port_%u_inflight_credits", dsw_xstats_port_get_inflight_credits,
 	  false },
 	{ "port_%u_pending_releases", dsw_xstats_port_get_pending_releases,
-- 
2.17.1