drbd: Load balancing of read requests

New config option for the disk secition "read-balancing", with
the values: prefer-local, prefer-remote, round-robin, when-congested-remote.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

3 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/drbd.h b/include/linux/drbd.h
index 1e9f754b66ac..157ba3d74dc7 100644
--- a/include/linux/drbd.h
+++ b/include/linux/drbd.h
@@ -102,6 +102,14 @@ enum drbd_on_congestion {
         OC_DISCONNECT,
 };
 
+enum drbd_read_balancing {
+        RB_PREFER_LOCAL,
+        RB_PREFER_REMOTE,
+        RB_ROUND_ROBIN,
+        RB_LEAST_PENDING,
+        RB_CONGESTED_REMOTE,
+};
+
 /* KEEP the order, do not delete or insert. Only append. */
 enum drbd_ret_code {
         ERR_CODE_BASE           = 100,
diff --git a/include/linux/drbd_genl.h b/include/linux/drbd_genl.h
index 2e6cefefe5e5..826008f297fe 100644
--- a/include/linux/drbd_genl.h
+++ b/include/linux/drbd_genl.h
@@ -129,6 +129,7 @@ GENL_struct(DRBD_NLA_DISK_CONF, 3, disk_conf,
         __flg_field_def(18, DRBD_GENLA_F_MANDATORY,     disk_drain, DRBD_DISK_DRAIN_DEF)
         __flg_field_def(19, DRBD_GENLA_F_MANDATORY,     md_flushes, DRBD_MD_FLUSHES_DEF)
         __u32_field_def(20,     DRBD_GENLA_F_MANDATORY, disk_timeout, DRBD_DISK_TIMEOUT_DEF)
+        __u32_field_def(21,     0 /* OPTIONAL */,       read_balancing, DRBD_READ_BALANCING_DEF)
 )
 
 GENL_struct(DRBD_NLA_RESOURCE_OPTS, 4, res_opts,
diff --git a/include/linux/drbd_limits.h b/include/linux/drbd_limits.h
index 6d0a24331ed2..17ef66a5c114 100644
--- a/include/linux/drbd_limits.h
+++ b/include/linux/drbd_limits.h
@@ -161,6 +161,7 @@
 #define DRBD_RR_CONFLICT_DEF ASB_DISCONNECT
 #define DRBD_ON_NO_DATA_DEF OND_IO_ERROR
 #define DRBD_ON_CONGESTION_DEF OC_BLOCK
+#define DRBD_READ_BALANCING_DEF RB_PREFER_LOCAL
 
 #define DRBD_MAX_BIO_BVECS_MIN 0
 #define DRBD_MAX_BIO_BVECS_MAX 128