Implement a simple LRU block cache. By default this is initialised to 16k,

and will bypass transfers for more than 8k.  Blocks are invalidated after
2 seconds, so removable media should not confuse the cache.

The 8k threshold is a compromise; all UFS transfers performed by
libstand are 8k or less, so large file reads thrash the cache.
However many filesystem metadata operations are also performed using
8k blocks, so using a lower threshold gives poor performance.

Those of you with an eye for cache algorithms are welcome to tell me
how badly this one sucks; you can start with the 'bcachestats' command
which will print the contents of the cache and access statistics.

1 files changed, 10 insertions, 1 deletions

diff --git a/sys/boot/common/bootstrap.h b/sys/boot/common/bootstrap.h
index 2eb1d80..a373e35 100644
--- a/sys/boot/common/bootstrap.h
+++ b/sys/boot/common/bootstrap.h
@@ -23,7 +23,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id: bootstrap.h,v 1.14 1998/10/21 20:07:04 msmith Exp $
+ *	$Id: bootstrap.h,v 1.15 1998/10/22 20:20:50 msmith Exp $
  */
 
 #include <sys/types.h>
@@ -72,6 +72,15 @@ extern size_t	strlenout(vm_offset_t str);
 extern char	*strdupout(vm_offset_t str);
 
 /*
+ * Disk block cache
+ */
+struct bcache_devdata
+{
+    int         (*dv_strategy)(void *devdata, int rw, daddr_t blk, size_t size, void *buf, size_t *rsize);
+    void	*dv_devdata;
+};
+
+/*
  * Modular console support.
  */
 struct console