hpfs: implement prefetch to improve performance

This patch implements prefetch to improve performance.  It helps mostly
when scanning the bitmaps to calculate free space.

Signed-off-by: Mikulas Patocka <mpatocka@artax.karlin.mff.cuni.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 63 insertions, 5 deletions

diff --git a/fs/hpfs/buffer.c b/fs/hpfs/buffer.c
index f49d1498aa2e..4d0a1afa058c 100644
--- a/fs/hpfs/buffer.c
+++ b/fs/hpfs/buffer.c
@@ -7,8 +7,37 @@
  */
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/blkdev.h>
 #include "hpfs_fn.h"
 
+void hpfs_prefetch_sectors(struct super_block *s, unsigned secno, int n)
+{
+        struct buffer_head *bh;
+        struct blk_plug plug;
+
+        if (n <= 0 || unlikely(secno >= hpfs_sb(s)->sb_fs_size))
+                return;
+
+        bh = sb_find_get_block(s, secno);
+        if (bh) {
+                if (buffer_uptodate(bh)) {
+                        brelse(bh);
+                        return;
+                }
+                brelse(bh);
+        };
+
+        blk_start_plug(&plug);
+        while (n > 0) {
+                if (unlikely(secno >= hpfs_sb(s)->sb_fs_size))
+                        break;
+                sb_breadahead(s, secno);
+                secno++;
+                n--;
+        }
+        blk_finish_plug(&plug);
+}
+
 /* Map a sector into a buffer and return pointers to it and to the buffer. */
 
 void *hpfs_map_sector(struct super_block *s, unsigned secno, struct buffer_head **bhp,
@@ -18,6 +47,8 @@ void *hpfs_map_sector(struct super_block *s, unsigned secno, struct buffer_head
 
         hpfs_lock_assert(s);
 
+        hpfs_prefetch_sectors(s, secno, ahead);
+
         cond_resched();
 
         *bhp = bh = sb_bread(s, secno);
@@ -67,6 +98,8 @@ void *hpfs_map_4sectors(struct super_block *s, unsigned secno, struct quad_buffe
                 return NULL;
         }
 
+        hpfs_prefetch_sectors(s, secno, 4 + ahead);
+
         qbh->data = data = kmalloc(2048, GFP_NOFS);
         if (!data) {
                 printk("HPFS: hpfs_map_4sectors: out of memory\n");
diff --git a/fs/hpfs/hpfs_fn.h b/fs/hpfs/hpfs_fn.h
index b7ae286646b5..1b398636e990 100644
--- a/fs/hpfs/hpfs_fn.h
+++ b/fs/hpfs/hpfs_fn.h
@@ -27,8 +27,9 @@
 #define ALLOC_FWD_MAX   128
 #define ALLOC_M         1
 #define FNODE_RD_AHEAD  16
-#define ANODE_RD_AHEAD  16
-#define DNODE_RD_AHEAD  4
+#define ANODE_RD_AHEAD  0
+#define DNODE_RD_AHEAD  72
+#define COUNT_RD_AHEAD  62
 
 #define FREE_DNODES_ADD 58
 #define FREE_DNODES_DEL 29
@@ -207,6 +208,7 @@ void hpfs_remove_fnode(struct super_block *, fnode_secno fno);
 
 /* buffer.c */
 
+void hpfs_prefetch_sectors(struct super_block *, unsigned, int);
 void *hpfs_map_sector(struct super_block *, unsigned, struct buffer_head **, int);
 void *hpfs_get_sector(struct super_block *, unsigned, struct buffer_head **);
 void *hpfs_map_4sectors(struct super_block *, unsigned, struct quad_buffer_head *, int);
@@ -271,6 +273,7 @@ void hpfs_evict_inode(struct inode *);
 
 __le32 *hpfs_map_dnode_bitmap(struct super_block *, struct quad_buffer_head *);
 __le32 *hpfs_map_bitmap(struct super_block *, unsigned, struct quad_buffer_head *, char *);
+void hpfs_prefetch_bitmap(struct super_block *, unsigned);
 unsigned char *hpfs_load_code_page(struct super_block *, secno);
 __le32 *hpfs_load_bitmap_directory(struct super_block *, secno bmp);
 struct fnode *hpfs_map_fnode(struct super_block *s, ino_t, struct buffer_head **);
diff --git a/fs/hpfs/map.c b/fs/hpfs/map.c
index 803d3da3a0fe..3aa66ae1031e 100644
--- a/fs/hpfs/map.c
+++ b/fs/hpfs/map.c
@@ -17,6 +17,7 @@ __le32 *hpfs_map_bitmap(struct super_block *s, unsigned bmp_block,
                          struct quad_buffer_head *qbh, char *id)
 {
         secno sec;
+        __le32 *ret;
         unsigned n_bands = (hpfs_sb(s)->sb_fs_size + 0x3fff) >> 14;
         if (hpfs_sb(s)->sb_chk) if (bmp_block >= n_bands) {
                 hpfs_error(s, "hpfs_map_bitmap called with bad parameter: %08x at %s", bmp_block, id);
@@ -27,7 +28,23 @@ __le32 *hpfs_map_bitmap(struct super_block *s, unsigned bmp_block,
                 hpfs_error(s, "invalid bitmap block pointer %08x -> %08x at %s", bmp_block, sec, id);
                 return NULL;
         }
-        return hpfs_map_4sectors(s, sec, qbh, 4);
+        ret = hpfs_map_4sectors(s, sec, qbh, 4);
+        if (ret) hpfs_prefetch_bitmap(s, bmp_block + 1);
+        return ret;
+}
+
+void hpfs_prefetch_bitmap(struct super_block *s, unsigned bmp_block)
+{
+        unsigned to_prefetch, next_prefetch;
+        unsigned n_bands = (hpfs_sb(s)->sb_fs_size + 0x3fff) >> 14;
+        if (unlikely(bmp_block >= n_bands))
+                return;
+        to_prefetch = le32_to_cpu(hpfs_sb(s)->sb_bmp_dir[bmp_block]);
+        if (unlikely(bmp_block + 1 >= n_bands))
+                next_prefetch = 0;
+        else
+                next_prefetch = le32_to_cpu(hpfs_sb(s)->sb_bmp_dir[bmp_block + 1]);
+        hpfs_prefetch_sectors(s, to_prefetch, 4 + 4 * (to_prefetch + 4 == next_prefetch));
 }
 
 /*
diff --git a/fs/hpfs/super.c b/fs/hpfs/super.c
index 962e90c37aec..4334cda8dba1 100644
--- a/fs/hpfs/super.c
+++ b/fs/hpfs/super.c
@@ -121,7 +121,7 @@ unsigned hpfs_count_one_bitmap(struct super_block *s, secno secno)
         unsigned long *bits;
         unsigned count;
 
-        bits = hpfs_map_4sectors(s, secno, &qbh, 4);
+        bits = hpfs_map_4sectors(s, secno, &qbh, 0);
         if (!bits)
                 return 0;
         count = bitmap_weight(bits, 2048 * BITS_PER_BYTE);
@@ -134,8 +134,13 @@ static unsigned count_bitmaps(struct super_block *s)
         unsigned n, count, n_bands;
         n_bands = (hpfs_sb(s)->sb_fs_size + 0x3fff) >> 14;
         count = 0;
-        for (n = 0; n < n_bands; n++)
+        for (n = 0; n < COUNT_RD_AHEAD; n++) {
+                hpfs_prefetch_bitmap(s, n);
+        }
+        for (n = 0; n < n_bands; n++) {
+                hpfs_prefetch_bitmap(s, n + COUNT_RD_AHEAD);
                 count += hpfs_count_one_bitmap(s, le32_to_cpu(hpfs_sb(s)->sb_bmp_dir[n]));
+        }
         return count;
 }