[ofw] [PATCH] DAPL v2.0: common: increase default IB ack timer from 16 to 20

[Davis, Arlin R]

For larger, more congested fabrics, a larger ACK timer is needed.
Consumers can still change default with environment variable
DAPL_ACK_TIMER if they need to increase or decrease.

This applies to SCM and UCM providers only. The CMA provider, which
uses rdma_cm, has no way to control ack timer with current API.

Signed-off-by: Arlin Davis <***@intel.com>
---
dapl/openib_common/dapl_ib_common.h | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/dapl/openib_common/dapl_ib_common.h b/dapl/openib_common/dapl_ib_common.h
index a0dd772..e757b65 100644
--- a/dapl/openib_common/dapl_ib_common.h
+++ b/dapl/openib_common/dapl_ib_common.h
@@ -158,8 +158,8 @@ typedef uint16_t ib_hca_port_t;
#define DAT_UD_QKEY 0x78654321

/* RC timer - retry count defaults */
-#define DCM_ACK_TIMER 16 /* 5 bits, 4.096us*2^ack_timer. 16== 268ms */
-#define DCM_ACK_RETRY 7 /* 3 bits, 7 * 268ms = 1.8 seconds */
+#define DCM_ACK_TIMER 20 /* 5 bits, 4.096us*2^ack_timer. 16== 268ms, 20==4.2s */
+#define DCM_ACK_RETRY 7 /* 3 bits, 7 * 4.2 == 30 seconds */
#define DCM_RNR_TIMER 12 /* 5 bits, 12 =.64ms, 28 =163ms, 31 =491ms */
#define DCM_RNR_RETRY 7 /* 3 bits, 7 == infinite */
#define DCM_IB_MTU 204

[Hefty, Sean]

Post by Davis, Arlin R
For larger, more congested fabrics, a larger ACK timer is needed.
Consumers can still change default with environment variable
DAPL_ACK_TIMER if they need to increase or decrease.
This applies to SCM and UCM providers only. The CMA provider, which
uses rdma_cm, has no way to control ack timer with current API.

The rdma_cm uses the path lifetime to determine the QP timeout value. The path record can be manipulated by the user when

[Davis, Arlin R]

Post by Hefty, Sean

Post by Davis, Arlin R
For larger, more congested fabrics, a larger ACK timer is needed.
Consumers can still change default with environment variable
DAPL_ACK_TIMER if they need to increase or decrease.
This applies to SCM and UCM providers only. The CMA provider, which
uses rdma_cm, has no way to control ack timer with current API.

The rdma_cm uses the path lifetime to determine the QP timeout value.
The path record can be manipulated by the user when calling
rdma_create_ep().

I stand corrected. I guess I should have said "has no direct way".
Yes, a user can modify path lifetime via rdma_create_ep() but there
is no way for the user to know how much that will be manipulated and
increased in the IB CM d

[Hefty, Sean]

Post by Davis, Arlin R
Yes, a user can modify path lifetime via rdma_create_ep() but there
is no way for the user to know how much that will be manipulated and
increased in the IB CM driver.

Sure there is. It's an open source driver. :)

The ib_cm calculates the "correct" timeout based on the packet lifetime provided by the SA and the CA ack timeout. If user modifications to this value are necessary, th

[Davis, Arlin R]

Post by Hefty, Sean

Post by Davis, Arlin R
Yes, a user can modify path lifetime via rdma_create_ep() but there
is no way for the user to know how much that will be manipulated and
increased in the IB CM driver.

Sure there is. It's an open source driver. :)
The ib_cm calculates the "correct" timeout based on the packet lifetime
provided by the SA and the CA ack timeout. If user modifications to
this value are necessary, then there is a bug in either the SA or HCA
driver.

or there could be congestion on the fa