drivers: block: add block device cache

Add a block device cache to speed up repeated reads of block devices by
various filesystems.

This small amount of cache can dramatically speed up filesystem
operations by skipping repeated reads of common areas of a block
device (typically directory structures).

This has shown to have some benefit on FAT filesystem operations of
loading a kernel and RAM disk, but more dramatic benefits on ext4
filesystems when the kernel and/or RAM disk are spread across
multiple extent header structures as described in commit fc0fc50.

The cache is implemented through a minimal list (block_cache) maintained
in most-recently-used order and count of the current number of entries
(cache_count). It uses a maximum block count setting to prevent copies
of large block reads and an upper bound on the number of cached areas.

The maximum number of entries in the cache defaults to 32 and the maximum
number of blocks per cache entry has a default of 2, which has shown to
produce the best results on testing of ext4 and FAT filesystems.

The 'blkcache' command (enabled through CONFIG_CMD_BLOCK_CACHE) allows
changing these values and can be used to tune for a particular filesystem
layout.

Signed-off-by: Eric Nelson <eric@nelint.com>

1 files changed, 104 insertions, 1 deletions

diff --git a/include/blk.h b/include/blk.h
index e83c144..263a791 100644
--- a/include/blk.h
+++ b/include/blk.h
@@ -83,6 +83,97 @@ struct blk_desc {
 #define PAD_TO_BLOCKSIZE(size, blk_desc) \
 	(PAD_SIZE(size, blk_desc->blksz))
 
+#ifdef CONFIG_BLOCK_CACHE
+/**
+ * blkcache_read() - attempt to read a set of blocks from cache
+ *
+ * @param iftype - IF_TYPE_x for type of device
+ * @param dev - device index of particular type
+ * @param start - starting block number
+ * @param blkcnt - number of blocks to read
+ * @param blksz - size in bytes of each block
+ * @param buf - buffer to contain cached data
+ *
+ * @return - '1' if block returned from cache, '0' otherwise.
+ */
+int blkcache_read
+	(int iftype, int dev,
+	 lbaint_t start, lbaint_t blkcnt,
+	 unsigned long blksz, void *buffer);
+
+/**
+ * blkcache_fill() - make data read from a block device available
+ * to the block cache
+ *
+ * @param iftype - IF_TYPE_x for type of device
+ * @param dev - device index of particular type
+ * @param start - starting block number
+ * @param blkcnt - number of blocks available
+ * @param blksz - size in bytes of each block
+ * @param buf - buffer containing data to cache
+ *
+ */
+void blkcache_fill
+	(int iftype, int dev,
+	 lbaint_t start, lbaint_t blkcnt,
+	 unsigned long blksz, void const *buffer);
+
+/**
+ * blkcache_invalidate() - discard the cache for a set of blocks
+ * because of a write or device (re)initialization.
+ *
+ * @param iftype - IF_TYPE_x for type of device
+ * @param dev - device index of particular type
+ */
+void blkcache_invalidate
+	(int iftype, int dev);
+
+/**
+ * blkcache_configure() - configure block cache
+ *
+ * @param blocks - maximum blocks per entry
+ * @param entries - maximum entries in cache
+ */
+void blkcache_configure(unsigned blocks, unsigned entries);
+
+/*
+ * statistics of the block cache
+ */
+struct block_cache_stats {
+	unsigned hits;
+	unsigned misses;
+	unsigned entries; /* current entry count */
+	unsigned max_blocks_per_entry;
+	unsigned max_entries;
+};
+
+/**
+ * get_blkcache_stats() - return statistics and reset
+ *
+ * @param stats - statistics are copied here
+ */
+void blkcache_stats(struct block_cache_stats *stats);
+
+#else
+
+static inline int blkcache_read
+	(int iftype, int dev,
+	 lbaint_t start, lbaint_t blkcnt,
+	 unsigned long blksz, void *buffer)
+{
+	return 0;
+}
+
+static inline void blkcache_fill
+	(int iftype, int dev,
+	 lbaint_t start, lbaint_t blkcnt,
+	 unsigned long blksz, void const *buffer) {}
+
+static inline void blkcache_invalidate
+	(int iftype, int dev) {}
+
+#endif
+
 #ifdef CONFIG_BLK
 struct udevice;
 
@@ -224,23 +315,35 @@ int blk_unbind_all(int if_type);
 static inline ulong blk_dread(struct blk_desc *block_dev, lbaint_t start,
 			      lbaint_t blkcnt, void *buffer)
 {
+	ulong blks_read;
+	if (blkcache_read(block_dev->if_type, block_dev->devnum,
+			  start, blkcnt, block_dev->blksz, buffer))
+		return blkcnt;
+
 	/*
 	 * We could check if block_read is NULL and return -ENOSYS. But this
 	 * bloats the code slightly (cause some board to fail to build), and
 	 * it would be an error to try an operation that does not exist.
 	 */
-	return block_dev->block_read(block_dev, start, blkcnt, buffer);
+	blks_read = block_dev->block_read(block_dev, start, blkcnt, buffer);
+	if (blks_read == blkcnt)
+		blkcache_fill(block_dev->if_type, block_dev->devnum,
+			      start, blkcnt, block_dev->blksz, buffer);
+
+	return blks_read;
 }
 
 static inline ulong blk_dwrite(struct blk_desc *block_dev, lbaint_t start,
 			       lbaint_t blkcnt, const void *buffer)
 {
+	blkcache_invalidate(block_dev->if_type, block_dev->devnum);
 	return block_dev->block_write(block_dev, start, blkcnt, buffer);
 }
 
 static inline ulong blk_derase(struct blk_desc *block_dev, lbaint_t start,
 			       lbaint_t blkcnt)
 {
+	blkcache_invalidate(block_dev->if_type, block_dev->devnum);
 	return block_dev->block_erase(block_dev, start, blkcnt);
 }
 #endif /* !CONFIG_BLK */