diff options
author | Christopher Haster <chaster@utexas.edu> | 2018-08-04 22:48:27 +0300 |
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committer | Christopher Haster <chaster@utexas.edu> | 2018-10-16 16:32:01 +0300 |
commit | 3cfa08602a7087f84672f7cf53a2e59b22076b18 (patch) | |
tree | 367caea86a3ed380e649844a1efdb845d2ba24ee /lfs_util.h | |
parent | 97f35c3e05f3465c76216a918cd4792d875d6827 (diff) |
Introduced cache_size as alternative to hardware read/write sizes
The introduction of an explicit cache_size configuration allows
customization of the cache buffers independently from the hardware
read/write sizes.
This has been one of littlefs's main handicaps. Without a distinction
between cache units and hardware limitations, littlefs isn't able to
read or program _less_ than the cache size. This leads to the
counter-intuitive case where larger cache sizes can actually be harmful,
since larger read/prog sizes require sending more data over the bus if
we're only accessing a small set of data (for example the CTZ skip-list
traversal).
This is compounded with metadata logging, since a large program size
limits the number of commits we can write out in a single metadata
block. It really doesn't make sense to link program size + cache
size here.
With a separate cache_size configuration, we can be much smarter about
what we actually read/write from disk.
This also simplifies cache handling a bit. Before there were two
possible cache sizes, but these were rarely used. Note that the
cache_size is NOT written to the superblock and can be freely changed
without breaking backwards compatibility.
Diffstat (limited to 'lfs_util.h')
-rw-r--r-- | lfs_util.h | 6 |
1 files changed, 5 insertions, 1 deletions
@@ -183,8 +183,12 @@ static inline uint16_t lfs_tole16(uint16_t a) { } // Align to nearest multiple of a size +static inline uint32_t lfs_aligndown(uint32_t a, uint32_t alignment) { + return a - (a % alignment); +} + static inline uint32_t lfs_alignup(uint32_t a, uint32_t alignment) { - return (a + alignment-1) - ((a + alignment-1) % alignment); + return lfs_aligndown(a + alignment-1, alignment); } // Calculate CRC-32 with polynomial = 0x04c11db7 |