[Devel] [PATCH 2/4] fs/fuse kio: relax congestion avoidance limits (backport from usermode)

[Pavel Butsykin]

Investigation of VZ US-QA cluster shows that congestion window
reduction after idle periods results in too slow window open
after data start to flow again.

So, introduce ssthresh to allow faster window open after
idle periods.

Maybe, even this is not enough and window should be open
even more aggressively. Further observations will show.

Signed-off-by: Pavel Butsykin <pbutsykin at virtuozzo.com>
---
 fs/fuse/kio/pcs/pcs_cs.c  | 26 +++++++++++++++++++++-----
 fs/fuse/kio/pcs/pcs_cs.h  |  1 +
 fs/fuse/kio/pcs/pcs_map.c |  7 ++++++-
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_cs.c b/fs/fuse/kio/pcs/pcs_cs.c
index 00cd1ae99850..58ad6aea17b8 100644
--- a/fs/fuse/kio/pcs/pcs_cs.c
+++ b/fs/fuse/kio/pcs/pcs_cs.c
@@ -62,6 +62,7 @@ struct pcs_cs *pcs_cs_alloc(struct pcs_cs_set *css,
 	cs->in_flight = 0;
 	cs->cwnd = PCS_CS_INIT_CWND;
 	cs->eff_cwnd = PCS_CS_INIT_CWND;
+	cs->ssthresh = PCS_CS_INIT_CWND;
 	cs->cwr_state = 0;
 	atomic_set(&cs->latency_avg, 0);
 	cs->net_latency_avg = 0;
@@ -603,6 +604,10 @@ static void handle_congestion(struct pcs_cs *cs, struct pcs_rpc_hdr *h)
 		 * to half of min(in_flight, cwnd) and enter congestion reduction state,
 		 * where we ignore further congestion notifications until window is reduced
 		 */
+		if (who->cwnd >= PCS_CS_INIT_CWND)
+			who->ssthresh = who->cwnd;
+		else
+			who->ssthresh = PCS_CS_INIT_CWND;
 		if (who->in_flight < who->cwnd)
 			who->cwnd = who->in_flight;
 		who->cwnd /= 2;
@@ -659,8 +664,12 @@ static void cs_keep_waiting(struct pcs_rpc *ep, struct pcs_msg *req, struct pcs_
 		}
 
 		if (!who->cwr_state) {
-			FUSE_KDTRACE(cc_from_csset(cs->css)->fc, "Congestion window on CS" NODE_FMT " reducing %d/%d/%d", NODE_ARGS(h->xid.origin),
-				     who->in_flight, who->eff_cwnd, who->cwnd);
+			FUSE_KTRACE(cc_from_csset(cs->css)->fc, "Congestion window on CS" NODE_FMT " reducing %d/%d/%d", NODE_ARGS(h->xid.origin),
+				    who->in_flight, who->eff_cwnd, who->cwnd);
+			if (who->cwnd >= PCS_CS_INIT_CWND)
+				who->ssthresh = who->cwnd;
+			else
+				who->ssthresh = PCS_CS_INIT_CWND;
 			if (who->in_flight < who->cwnd)
 				who->cwnd = who->in_flight;
 			who->cwnd /= 2;
@@ -899,9 +908,14 @@ unsigned int cs_get_avg_in_flight(struct pcs_cs *cs)
 				cs->in_flight_avg >>= interval;
 			}
 			if (cs->cwnd > PCS_CS_INIT_CWND) {
-				cs->cwnd = PCS_CS_INIT_CWND;
-				if (cs->eff_cwnd > PCS_CS_INIT_CWND)
-					cs->eff_cwnd = PCS_CS_INIT_CWND;
+				unsigned int cwnd = PCS_CS_INIT_CWND;
+				TRACE("Congestion window on CS#" NODE_FMT " was not used, shrink %u -> %u", NODE_ARGS(cs->id),
+					cs->cwnd, cwnd);
+				if (cs->cwnd > cs->ssthresh)
+					cs->ssthresh = cs->cwnd;
+				cs->cwnd = cwnd;
+				if (cs->eff_cwnd > cwnd)
+					cs->eff_cwnd = cwnd;
 			}
 		}
 	}
@@ -962,6 +976,8 @@ void cs_cwnd_use_or_lose(struct pcs_cs *cs)
 
 			FUSE_KTRACE(cc_from_csset(cs->css)->fc, "Congestion window on CS#" NODE_FMT " was not used, shrink %u -> %u", NODE_ARGS(cs->id),
 				    cs->cwnd, cwnd);
+			if (cs->cwnd > cs->ssthresh)
+				cs->ssthresh = cs->cwnd;
 			cs->cwnd = cwnd;
 			if (cs->eff_cwnd > cwnd)
 				cs->eff_cwnd = cwnd;
diff --git a/fs/fuse/kio/pcs/pcs_cs.h b/fs/fuse/kio/pcs/pcs_cs.h
index 1fb40936d046..513d53539211 100644
--- a/fs/fuse/kio/pcs/pcs_cs.h
+++ b/fs/fuse/kio/pcs/pcs_cs.h
@@ -52,6 +52,7 @@ struct pcs_cs {
 	unsigned int		in_flight;
 	unsigned int		eff_cwnd;
 	unsigned int		cwnd;
+	unsigned int            ssthresh;
 	int			cwr_state;
 	atomic_t		latency_avg;
 	unsigned int		net_latency_avg;
diff --git a/fs/fuse/kio/pcs/pcs_map.c b/fs/fuse/kio/pcs/pcs_map.c
index 0af852615ff4..9c3762c92315 100644
--- a/fs/fuse/kio/pcs/pcs_map.c
+++ b/fs/fuse/kio/pcs/pcs_map.c
@@ -1414,6 +1414,11 @@ static void pcs_cs_deaccount(struct pcs_int_request *ireq, struct pcs_cs * cs, i
 		if (cs->last_latency > iolat_cutoff && ireq->type != PCS_IREQ_FLUSH) {
 			unsigned int clamp;
 
+			if (cs->cwnd >= PCS_CS_INIT_CWND)
+				cs->ssthresh = cs->cwnd;
+			else
+				cs->ssthresh = PCS_CS_INIT_CWND;
+
 			clamp = PCS_CS_INIT_CWND;
 			if (cs->last_latency > iolat_cutoff*8)
 				clamp = PCS_CS_INIT_CWND/8;
@@ -1429,7 +1434,7 @@ static void pcs_cs_deaccount(struct pcs_int_request *ireq, struct pcs_cs * cs, i
 		} else if (cs->in_flight >= cs->cwnd && !cs->cwr_state && worth_to_grow(ireq, cs)) {
 			unsigned int cwnd;
 
-			if (cs->cwnd < PCS_CS_INIT_CWND)
+			if (cs->cwnd <= cs->ssthresh)
 				cwnd = cs->cwnd + cost;
 			else
 				cwnd = cs->cwnd + 0x100000000ULL/cs->cwnd;
-- 
2.15.1