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+## Gas Balancing
+
+The gas balancing process targets to set gas costs of syscalls to be in line with
+10 gas per nanosecond on reference hardware.
+The process can be either performed for all syscalls based on existing messages and chain or targeted
+at single syscall.
+
+#### Reference hardware
+
+The reference hardware is TR3970x with 128GB of RAM. This is what was available at the time and
+may be subject to change.
+
+### Complete gas balancing
+
+Complete gas balancing is performed using `lotus-bench` the process is based on importing a chain export
+and collecting gas traces which are later aggregated.
+
+Before building `lotus-bench` make sure `EnableGasTracing` in `chain/vm/runtime.go` is set to `true`.
+
+The process can be started using `./lotus-bench import` with `--car` flag set to the location of
+CAR chain export. `--start-epoch` and `--end-epoch` can be used to to limit the range of epochs to run
+the benchmark. Note that state tree of `start-epoch` needs to be in the CAR file or has to be previously computed
+to work.
+
+The output will be a `bench.json` file containing information about every syscall invoked
+and the time taken by these invocations. This file can grow to be quite big in size so make sure you have
+spare space.
+
+After the bench run is complete the `bench.json` file can be analyzed with `./lotus-bench import analyze bench.json`.
+
+It will compute means, standard deviations and co-variances (when applicable) of syscall runtimes. 
+The output is in nanoseconds, so the gas values for syscalls should be 10x that. In cases where co-variance of
+execution time to some parameter is evaluated, the strength of the correlation should be taken into account.
+
+#### Special cases
+
+OnImplPut compute gas is based on the flush time to disk of objects created,
+during block execution (when gas traces are formed) objects are only written to memory. Use `vm/flush_copy_ms` and  `vm/flush_copy_count` to estimate OnIpldPut compute cost.
+
+
+### Targeted gas balancing
+
+In some cases complete gas balancing is infeasible, either new syscall gets introduced or
+complete balancing is too time consuming.
+
+In these cases the recommended way to estimate gas for given syscall is to perform an `in-vivo` benchmark.
+In the past `in-vitro` as in standalone benchmarks were found to be highly inaccurate when compared to results
+of real execution.
+
+A in-vivo benchmark can be performed by running an example of such syscall during block execution.
+The best place to hook-in such benchmark is message execution loop in
+`chain/stmgr/stmgr.go` in `ApplyBlocks()`. Depending of time required to complete the syscall it might be
+advisable to run the execution only once every few messages.
+