User Manual

Driver FeaturesRev 2.1-1.0.6

Mellanox Technologies

4.6.2.4 Querying the Hardware Time

Querying the hardware for time is done via the

ibv_query_values_ex verb.

For example:

To change the queried time in nanoseconds resolution, use the

IBV_VALUES_HW_CLOCK_NS flag

along with the

hwclock_ns field.

4.7 Atomic Operations

Atomic Operations are applicable to the mlx4 driver only.

4.7.1 Enhanced Atomic Operations

ConnectX® implements a set of Extended Atomic Operations beyond those defined by the IB

spec. Atomicity guarantees, Atomic Ack generation, ordering rules and error behavior for this set

of extended Atomic operations is the same as that for IB standard Atomic operations (as defined

in section 9.4.5 of the IB spec).

4.7.1.1 Masked Compare and Swap (MskCmpSwap)

The MskCmpSwap atomic operation is an extension to the CmpSwap operation defined in the IB

spec. MskCmpSwap allows the user to select a portion of the 64 bit target data for the "compare"

check as well as to restrict the swap to a (possibly different) portion. The pseudocode below

describes the operation:

CQs that are opened with the ibv_create_cq_ex versb should be always be polled with

the ibv_poll_cq_ex verb.

ret = ibv_query_values_ex(context, IBV_VALUES_HW_CLOCK, &queried_values);

if (!ret && queried_values.comp_mask & IBV_VALUES_HW_CLOCK)

queried_time = queried_values.hwclock;

ret = ibv_query_values_ex(context, IBV_VALUES_HW_CLOCK_NS, &queried_values);

if (!ret && queried_values.comp_mask & IBV_VALUES_HW_CLOCK_NS)

queried_time_ns = queried_values.hwclock_ns;

Querying the Hardware Time is available only on physical functions / native machines.

| atomic_response = *va

| if (!((compare_add ^ *va) & compare_add_mask)) then