Changeset dba4a23 in mainline for uspace/srv/fs/fat/fat_fat.c

Timestamp:

2010-07-28T15:22:22Z (16 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

4637c72, 9a1d8ab

Parents:

6da81e0

Message:

Speed up sequential I/O by caching the "current" cluster in fat_block_get().
This improves sequentil read of a 5m file (using the cat command) by 45 seconds
(73s → 28s).

File:

• uspace/srv/fs/fat/fat_fat.c (modified) (4 diffs)

uspace/srv/fs/fat/fat_fat.c

@@ -142 +142 @@
     aoff64_t bn, int flags)
 {
+        fat_cluster_t firstc = nodep->firstc;
+        fat_cluster_t currc;
+        aoff64_t relbn = bn;
+        int rc;
+
         if (!nodep->size)
                 return ELIMIT;
@@ -158 +163 @@
         }
 
+        if (nodep->currc_cached_valid && bn >= nodep->currc_cached_bn) {
+                /*
+                 * We can start with the cluster cached by the previous call to
+                 * fat_block_get().
+                 */
+                firstc = nodep->currc_cached_value;
+                relbn -= (nodep->currc_cached_bn / SPC(bs)) * SPC(bs);
+        }
+
 fall_through:
-        return _fat_block_get(block, bs, nodep->idx->dev_handle, nodep->firstc,
-            NULL, bn, flags);
+        rc = _fat_block_get(block, bs, nodep->idx->dev_handle, firstc,
+            &currc, relbn, flags);
+        if (rc != EOK)
+                return rc;
+        
+        /*
+         * Update the "current" cluster cache.
+         */
+        nodep->currc_cached_valid = true;
+        nodep->currc_cached_bn = bn;
+        nodep->currc_cached_value = currc;
+
+        return rc;
 }
 
@@ -567 +592 @@
         dev_handle_t dev_handle = nodep->idx->dev_handle;
 
+        /*
+         * Invalidate cached cluster numbers.
+         */
         nodep->lastc_cached_valid = false;
+        if (nodep->currc_cached_value != lcl)
+                nodep->currc_cached_valid = false;
+
         if (lcl == FAT_CLST_RES0) {
                 /* The node will have zero size and no clusters allocated. */
@@ -597 +628 @@
         }
 
+        /*
+         * Update and re-enable the last cluster cache.
+         */
         nodep->lastc_cached_valid = true;
         nodep->lastc_cached_value = lcl;