VFLASHSIM / Flash Playground

This is the code associated with the short paper "Simulation-Based Performance Characterization of Common NOR Flash File Systems".

What it does

This is a simulator for evaluating the performance of embedded flash file systems. It models the interface to SPI NOR flash (see flash.hpp), with a DRAM region as the flash storage and read/write/erase functions for guarded access to the memory. At this interface, the simulator collects statistics about read/write/erase operations and their sizes. Together with timing information from flash chip datasheets, the latency for workloads can be estimated from the operation statistics. Currently, streaming read and write as well as compression are available as workload benchmarks (see bench.hpp). The available flash file systems are LittleFS, SPIFFS, NF2FS, and YAFFS2.

Requirements

For stack trace generation, cpptrace is required (and with it libdwarf). This is included in the devshell flake.nix and the Dockerfile.

After running a benchmark compiled with TRACE_OPS=1 (see flame_sampler.hpp), the corresponding flame graph can be created as follows:

flamegraph.pl stacks.folded > flamegraph.svg

This requires Brendan Gregg's flame graph scripts, which are also included in the devshell flake.nix.

Quick start

Clone with submodules:

git clone --recursive git@github.com:2ck/flash-playground.git

Set up YAFFS (one time step):

pushd .
cd yaffs2
git apply ../yaffs_smaller_header.patch
cd direct
./handle_common.sh copy
popd

Build and run:

make run # *or*
make docker-run

Configuration

Many values can be adapted at runtime via environment variables, for example:

FS=YAFFS START_SIZE=4096 ITS=1 BENCH=compress make run

This will run the compress benchmark for YAFFS once with a file size of 4KiB.

The following table lists all supported environment variables:

group	variable	default	description
flash	FLASH_SIZE	MiB(128)	total flash size in bytes
	FLASH_PAGE_SIZE	256	size of largest write unit
	FLASH_SECTOR_SIZE	KiB(4)	size of flash erase unit
	FLASH_READ_GRANULARITY	BYTE_WISE	whether chunks < page_size can be read
	FLASH_WRITE_GRANULARITY	BYTE_WISE	whether chunks < page_size can be written
benchmarks	FS	LFS	one of "LFS", "SPIFFS", "NF2FS", "YAFFS"
	BENCH	write	one of "gc" (garbage collection), "mount_test" (just the FS mount process), "write"/"write_parallel" (write to one/multiple open files), "read", "compress" (read from one file and write half of each chunk to another), "open_close"
	START_SIZE	1024	size of first benchmark operation, n-th iteration will have size n * START_SIZE
	ITS	64	iterations
	PRE_FILL	0	percentage of dirty pages to reach before benchmark
	KEEP_FILES	false	whether to delete/unlink files used to pre-fill
	CHUNK_SIZE	page_size	flash read/write chunk size
misc.	PRINT_MALLOC_STATS	false	whether to output static and dynamic memory usage by FS