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>

diff --git a/fs/hpfs/buffer.c b/fs/hpfs/buffer.c
index f49d149..4d0a1af 100644 (file)
--- 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 b7ae286..1b39863 100644 (file)
--- 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 803d3da..3aa66ae 100644 (file)
--- 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 962e90c..4334cda 100644 (file)
--- 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;
 }