SPARC System Specific Parameters

The following parameters apply to sun4v and SPARC M-Series sun4u platforms.

tsb_alloc_hiwater_factor

Description

Initializes tsb_alloc_hiwater to impose an upper limit on the amount of physical memory that can be allocated for translation storage buffers (TSBs) as follows:

tsb_alloc_hiwater = physical memory (bytes) / tsb_alloc_hiwater_factor

When the memory that is allocated to TSBs is equal to the value of tsb_alloc_hiwater, the TSB memory allocation algorithm attempts to reclaim TSB memory as pages are unmapped.

Exercise caution when using this factor to increase the value of tsb_alloc_hiwater. To prevent system hangs, the resulting high water value must be considerably lower than the value of swapfs_minfree and segspt_minfree.

Data Type

Integer

Default

32

Range

1 to MAXINIT

Note that a factor of 1 makes all physical memory available for allocation to TSBs, which could cause the system to hang. A factor that is too high will not leave memory available for allocation to TSBs, decreasing system performance.

Dynamic?

Yes

Validation

None

When to Change

Change the value of this parameter if the system has many processes that attach to very large shared memory segments. Under most circumstances, tuning of this variable is not necessary.

Commitment Level

Unstable

default_tsb_size

Description

Selects size of the initial translation storage buffers (TSBs) allocated to all processes.

Data Type

Integer

Default

Default is 0 (8 KB), which corresponds to 512 entries

Range

Possible values are:

Value Description 0 8 KB 1 16 KB 3 32 KB 4 128 KB 5 256 KB 6 512 KB 7 1 Mbyte

Dynamic?

Yes

Validation

None

When to Change

Generally, you do not need to change this value. However, doing so might provide some advantages if the majority of processes on the system have a larger than average working set, or if resident set size (RSS) sizing is disabled.

Commitment Level

Unstable

enable_tsb_rss_sizing

Description

Enables a resident set size (RSS) based TSB sizing heuristic.

Data Type

Boolean

Default

1 (TSBs can be resized)

Range

0 (TSBs remain at tsb_default_size) or 1 (TSBs can be resized)

If set to 0, then tsb_rss_factor is ignored.

Dynamic?

Yes

Validation

Yes

When to Change

Can be set to 0 to prevent growth of the TSBs. Under most circumstances, this parameter should be left at the default setting.

Commitment Level

Unstable

tsb_rss_factor

Description

Controls the RSS to TSB span ratio of the RSS sizing heuristic. This factor divided by 512 yields the percentage of the TSB span which must be resident in memory before the TSB is considered as a candidate for resizing.

Data Type

Integer

Default

384, resulting in a value of 75%. Thus, when the TSB is 3/4 full, its size will be increased. Note that some virtual addresses typically map to the same slot in the TSB. Therefore, conflicts can occur before the TSB is at 100% full.

Range

0 to 512

Dynamic?

Yes

Validation

None

When to Change

If the system is experiencing an excessive number of traps due to TSB misses, for example, due to virtual address conflicts in the TSB, you might consider decreasing this value toward 0.

For example, changing tsb_rss_factor to 256 (effectively, 50%) instead of 384 (effectively, 75%) might help eliminate virtual address conflicts in the TSB in some cases, but will use more kernel memory, particularly on a heavily loaded system.

TSB activity can be monitored with the trapstat -T command.

Commitment Level

Unstable