diff options
| -rw-r--r-- | Documentation/mm/damon/design.rst | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst index 667775bab86c..dd7e0f63a69a 100644 --- a/Documentation/mm/damon/design.rst +++ b/Documentation/mm/damon/design.rst @@ -203,6 +203,8 @@ This scheme, however, cannot preserve the quality of the output if the assumption is not guaranteed. +.. _damon_design_adaptive_regions_adjustment: + Adaptive Regions Adjustment ~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -264,6 +266,52 @@ tracepoints. For more details, please refer to the documentations for respectively. +Monitoring Parameters Tuning Guide +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In short, set ``aggregation interval`` to capture meaningful amount of accesses +for the purpose. The amount of accesses can be measured using ``nr_accesses`` +and ``age`` of regions in the aggregated monitoring results snapshot. The +default value of the interval, ``100ms``, turns out to be too short in many +cases. Set ``sampling interval`` proportional to ``aggregation interval``. By +default, ``1/20`` is recommended as the ratio. + +``Aggregation interval`` should be set as the time interval that the workload +can make an amount of accesses for the monitoring purpose, within the interval. +If the interval is too short, only small number of accesses are captured. As a +result, the monitoring results look everything is samely accessed only rarely. +For many purposes, that would be useless. If it is too long, however, the time +to converge regions with the :ref:`regions adjustment mechanism +<damon_design_adaptive_regions_adjustment>` can be too long, depending on the +time scale of the given purpose. This could happen if the workload is actually +making only rare accesses but the user thinks the amount of accesses for the +monitoring purpose too high. For such cases, the target amount of access to +capture per ``aggregation interval`` should carefully reconsidered. Also, note +that the captured amount of accesses is represented with not only +``nr_accesses``, but also ``age``. For example, even if every region on the +monitoring results show zero ``nr_accesses``, regions could still be +distinguished using ``age`` values as the recency information. + +Hence the optimum value of ``aggregation interval`` depends on the access +intensiveness of the workload. The user should tune the interval based on the +amount of access that captured on each aggregated snapshot of the monitoring +results. + +Note that the default value of the interval is 100 milliseconds, which is too +short in many cases, especially on large systems. + +``Sampling interval`` defines the resolution of each aggregation. If it is set +too large, monitoring results will look like every region was samely rarely +accessed, or samely frequently accessed. That is, regions become +undistinguishable based on access pattern, and therefore the results will be +useless in many use cases. If ``sampling interval`` is too small, it will not +degrade the resolution, but will increase the monitoring overhead. If it is +appropriate enough to provide a resolution of the monitoring results that +sufficient for the given purpose, it shouldn't be unnecessarily further +lowered. It is recommended to be set proportional to ``aggregation interval``. +By default, the ratio is set as ``1/20``, and it is still recommended. + + .. _damon_design_damos: Operation Schemes |