User Manual

Rev 2.2-1.0.1
Mellanox Technologies
105
4.10.4 Setting Performance Tuning
Use 4K MTU over OpenSM. For further information, please refer to Section 8.4.1,
“File Format”, on page 173
Default=0xffff, ipoib, mtu=5 : ALL=full;
Use MTU for 4K (4092 Bytes):
In UD mode, the maximum MTU value is 4092 Bytes
Make sure that all interfaces (including the guest interface and its virtual bridge) have the same
MTU value (MTU 4092 Bytes). For further information of MTU settings, please refer to the
Hypervisor User Manual.
Tune the TCP/IP stack using sysctl (dom0/domu)
# /sbin/sysctl_perf_tuning
Other performance tuning for KVM environment such as vCPU pinning and NUMA
tuning may apply. For further information, please refer to the Hypervisor User Manual.
4.11 Contiguous Pages
Contiguous Pages improves performance by allocating user memory regions over physical con-
tiguous pages. It enables a user application to ask low level drivers to allocate contiguous mem-
ory for it as part of
ibv_reg_mr.
Additional performance improvements can be reached by allocating Queue Pair (QP) and Com-
pletion Queue (CQ|) buffers to the Contiguous Pages.
To activate set the below environment variables with values of PREFER_CONTIG or CONTIG.
For QP: MLX_QP_ALLOC_TYPE
For CQ: MLX_CQ_ALLOC_TYPE
The following are all the possible values that can be allocated to the buffer:
Table 5 - Buffer Values
Possible Value
1
1. Values are NOT case sensitive.
ANON Use current pages ANON small ones.
HUGE Force huge pages.
CONTIG Force contiguous pages.
PREFER_CONTIG Try contiguous fallback to ANON small pages. (Default)
PREFER_HUGE Try huge fallback to ANON small pages.
ALL Try huge fallback to contiguous if failed fallback to ANON small pages.
Usage:
The application calls the
ibv_exp_reg_mr API which turns on the
IBV_EXP_ACCESS_ALLOCATE_MR bit and sets the input address to NULL. Upon success, the
Description