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.

2 files changed, 18 insertions, 2 deletions

diff --git a/sys/boot/i386/libi386/biosdisk.c b/sys/boot/i386/libi386/biosdisk.c
index b4c7769..502d3be 100644
--- a/sys/boot/i386/libi386/biosdisk.c
+++ b/sys/boot/i386/libi386/biosdisk.c
@@ -23,7 +23,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id: biosdisk.c,v 1.15 1998/10/30 07:15:52 luoqi Exp $
+ *	$Id: biosdisk.c,v 1.16 1998/10/31 02:53:11 msmith Exp $
  */
 
 /*
@@ -103,6 +103,7 @@ static int	bd_int13probe(struct bdinfo *bd);
 
 static int	bd_init(void);
 static int	bd_strategy(void *devdata, int flag, daddr_t dblk, size_t size, void *buf, size_t *rsize);
+static int	bd_realstrategy(void *devdata, int flag, daddr_t dblk, size_t size, void *buf, size_t *rsize);
 static int	bd_open(struct open_file *f, ...);
 static int	bd_close(struct open_file *f);
 static void	bd_print(int verbose);
@@ -495,6 +496,16 @@ bd_closedisk(struct open_disk *od)
 static int 
 bd_strategy(void *devdata, int rw, daddr_t dblk, size_t size, void *buf, size_t *rsize)
 {
+    struct bcache_devdata	bcd;
+    
+    bcd.dv_strategy = bd_realstrategy;
+    bcd.dv_devdata = devdata;
+    return(bcache_strategy(&bcd, rw, dblk, size, buf, rsize));
+}
+
+static int 
+bd_realstrategy(void *devdata, int rw, daddr_t dblk, size_t size, void *buf, size_t *rsize)
+{
     struct open_disk	*od = (struct open_disk *)(((struct i386_devdesc *)devdata)->d_kind.biosdisk.data);
     int			blks;
 #ifdef BD_SUPPORT_FRAGS
diff --git a/sys/boot/i386/loader/main.c b/sys/boot/i386/loader/main.c
index 2e0ed80..dfd1bff 100644
--- a/sys/boot/i386/loader/main.c
+++ b/sys/boot/i386/loader/main.c
@@ -23,7 +23,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id: main.c,v 1.12 1998/10/21 20:10:33 msmith Exp $
+ *	$Id: main.c,v 1.13 1998/10/22 20:23:58 msmith Exp $
  */
 
 /*
@@ -98,6 +98,11 @@ main(void)
     cons_probe();
 
     /*
+     * Initialise the block cache
+     */
+    bcache_init(32, 512);	/* 16k cache XXX tune this */
+
+    /*
      * March through the device switch probing for things.
      */
     for (i = 0; devsw[i] != NULL; i++)