net/rds: Fix endless RNR situation

Working with the following SRs:

	Exadata SR# 3-15640329311
	Linux SR#3-15675579325

it was discovered that by inserting IB_SEND_SOLICITED at regular
intervals removed the endless RNR Retry situation. The test was made
by inserting IB_SEND_SOLICITED at the same interval as
IB_SEND_SIGNALED was inserted, that is, by default for every 17th
fragment.

This commit introduces the sysctl variable
net.rds.ib.max_unsolicited_wr. A value of zero disables the
functionality of inserting IB_SEND_SOLICITED. A value of N will insert
IB_SEND_SOLICITED for every Nth fragment.

net.rds.ib.max_unsolicited_wr is by default 16, in order to avoid
customization when this fix is applied at the customer site.

This fix also has the nice side-effect that it improves IOPS for 1Q,
1D, 1T cases:

-q 1M -a 256:

Without fix:

tsks   tx/s   rx/s  tx+rx K/s    mbi K/s    mbo K/s tx us/c   rtt us cpu %
   1   1161      0 1189243.20       0.00       0.00  203.52   857.34 -1.00
(average)

With fix (with default net.rds.ib.max_unsolicited_wr = 16):

tsks   tx/s   rx/s  tx+rx K/s    mbi K/s    mbo K/s tx us/c   rtt us cpu %
   1   1323      0 1355849.36       0.00       0.00  203.76   751.50 -1.00
(average)

-q $[32*1024+256] -a 256:

With fix (net.rds.ib.max_unsolicited_wr = 0, i.e. disabled):

tsks   tx/s   rx/s  tx+rx K/s    mbi K/s    mbo K/s tx us/c   rtt us cpu %
   1  15243      0  492547.75       0.00       0.00   10.58    62.01 -1.00
(average)

Ditto with net.rds.ib.max_unsolicited_wr = 4 (two SEND_SOLICITED per ~32K):

tsks   tx/s   rx/s  tx+rx K/s    mbi K/s    mbo K/s tx us/c   rtt us cpu %
   1  16422      0  530641.03       0.00       0.00   10.28    57.25 -1.00
(average)

Orabug: 28857027

Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/net/rds/ib.h b/net/rds/ib.h
index 07daeb4df6c0eb8827ea6aeb8a2e0d8fc59a9a19..bd8eea05cb8599bd235e84a77579785d502971d5 100644 (file)
--- a/net/rds/ib.h
+++ b/net/rds/ib.h
@@ -255,6 +255,9 @@ struct rds_ib_connection {
 
        /* Batched completions */
        unsigned int            i_unsignaled_wrs;
+
+       /* Wake up receiver once in a while */
+       unsigned int            i_unsolicited_wrs;
        u8                      i_sl;
 
        atomic_t                i_cache_allocs;
@@ -747,6 +750,7 @@ void rds_ib_sysctl_exit(void);
 extern unsigned long rds_ib_sysctl_max_send_wr;
 extern unsigned long rds_ib_sysctl_max_recv_wr;
 extern unsigned long rds_ib_sysctl_max_unsig_wrs;
+extern unsigned long rds_ib_sysctl_max_unsolicited_wrs;
 extern unsigned long rds_ib_sysctl_max_unsig_bytes;
 extern unsigned long rds_ib_sysctl_max_recv_allocation;
 extern unsigned int rds_ib_sysctl_flow_control;

diff --git a/net/rds/ib_send.c b/net/rds/ib_send.c
index 462d88ee6a4d12b06620ce165451b7dd1a30d446..5d1a127de6cf4cbf4ff93962e4125369120f72a5 100644 (file)
--- a/net/rds/ib_send.c
+++ b/net/rds/ib_send.c
@@ -535,9 +535,15 @@ static inline int rds_ib_set_wr_signal_state(struct rds_ib_connection *ic,
        if (ic->i_unsignaled_wrs-- == 0 || notify) {
                ic->i_unsignaled_wrs = rds_ib_sysctl_max_unsig_wrs;
                send->s_wr.send_flags |= IB_SEND_SIGNALED;
-               return 1;
        }
-       return 0;
+
+       /* To keep the rx pipeline going, add SEND_SOLIICITED once in a while */
+       if (rds_ib_sysctl_max_unsolicited_wrs && --ic->i_unsolicited_wrs == 0) {
+               ic->i_unsolicited_wrs = rds_ib_sysctl_max_unsolicited_wrs;
+               send->s_wr.send_flags |= IB_SEND_SOLICITED;
+       }
+
+       return !!(send->s_wr.send_flags & IB_SEND_SIGNALED);
 }
 
 /*
@@ -642,6 +648,7 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
                        rm->data.op_count = 0;
                }
 
+               ic->i_unsolicited_wrs = rds_ib_sysctl_max_unsolicited_wrs;
                rds_message_addref(rm);
                rm->data.op_dmasg = 0;
                rm->data.op_dmaoff = 0;

diff --git a/net/rds/ib_sysctl.c b/net/rds/ib_sysctl.c
index 5515ee743acf71ad4749ce73a5baa0fa7ba6c501..2e08386548b5f24cf48dccadd836eaf0557c625a 100644 (file)
--- a/net/rds/ib_sysctl.c
+++ b/net/rds/ib_sysctl.c
@@ -49,6 +49,16 @@ unsigned long rds_ib_sysctl_max_unsig_wrs = 16;
 static unsigned long rds_ib_sysctl_max_unsig_wr_min = 1;
 static unsigned long rds_ib_sysctl_max_unsig_wr_max = 64;
 
+unsigned long rds_ib_sysctl_max_unsolicited_wrs = 16;
+
+/* Zero means inserting SEND_SOLICITED in the middle of an RDS message
+ * is disabled
+ */
+static unsigned long rds_ib_sysctl_max_unsolicited_wr_min;
+/* Nmbr frags of 1MB + 256B RDBMS hdr */
+static unsigned long rds_ib_sysctl_max_unsolicited_wr_max =
+       (1 * 1024 * 1024 + RDS_FRAG_SIZE) / RDS_FRAG_SIZE;
+
 /*
  * This sysctl does nothing.
  *
@@ -106,6 +116,15 @@ static struct ctl_table rds_ib_sysctl_table[] = {
                .extra1         = &rds_ib_sysctl_max_unsig_wr_min,
                .extra2         = &rds_ib_sysctl_max_unsig_wr_max,
        },
+       {
+               .procname       = "max_unsolicited_wr",
+               .data           = &rds_ib_sysctl_max_unsolicited_wrs,
+               .maxlen         = sizeof(unsigned long),
+               .mode           = 0644,
+               .proc_handler   = &proc_doulongvec_minmax,
+               .extra1         = &rds_ib_sysctl_max_unsolicited_wr_min,
+               .extra2         = &rds_ib_sysctl_max_unsolicited_wr_max,
+       },
        {
                .procname       = "max_recv_allocation",
                .data           = &rds_ib_sysctl_max_recv_allocation,