hello,
On Wed, Feb 09, 2005 at 12:59:17PM -0500, Tom Evans wrote:
>
> Hi All -
>
> I am new to the list - I have been using Reiser4 on Linux/Alpha
> for several months now and like very much what it offers.
>
> (I use a -mm kernel from kernel.org with a Debian distro)
>
> Recently I became aware or a large number or alignment fixups
> occurring in the kernel, specifically in the reiser4 code.
>
> (My machine(s) would occasionally slow to a crawl when doing
> intense disk i/o - I thought it was because I had recently
> started using IDE drives in my systems (the IDE controllers
> on these boards are notoriously slow) ).
>
> I determined that 50k+ alignment faults were happening
> per second - I traced the majority down to these 3 functions:
>
> 1) reiser4_find_next_set_bit (in fs/reiser4/plugins/space/bitmap.c)
> 2) find_next_zero_bit (in asm/bitops.h)
> 3) replace_extent (in fs/reiser4/plugins/item/extent.c)
>
> The first 2 accounted for ~4million faults during boot - essentially,
> the base address of the bit array is not aligned properly
> for ulong accesses on Alpha (which are 64bit).
>
> I worked around this by using "get_unaligned()" for the array
> accesses in #1 and implemented a version of "find_next_zero_bit"
> local to reiser4 that handles unaligned base addresses (no need
> for all other users of the function to suffer the same performance hit).
>
> Those 2 changes brought the number of alignment fixups to 0 on a boot -
> the #3 issue accounts for a very small number of fixups - I have not
> yet found the exact location.
>
> While these changes eliminated the faults, they are not optimal,
> get_unaligned() adds many cycles over a standard load.
>
> I wanted to see if anyone here was already familiar with this issue and
> what the process would be for getting it addressed.
it is known. ca you try the attached patch?
>
> Thanks for your patience!
>
> ...tom
>
--
Alex.
===== plugin/space/bitmap.c 1.186 vs edited =====
--- 1.186/plugin/space/bitmap.c Wed Jan 19 18:52:52 2005
+++ edited/plugin/space/bitmap.c Sun Feb 6 19:23:01 2005
@@ -54,13 +54,15 @@
#define CHECKSUM_SIZE 4
+#define BYTES_PER_LONG (sizeof(long))
+
#if BITS_PER_LONG == 64
# define LONG_INT_SHIFT (6)
#else
# define LONG_INT_SHIFT (5)
#endif
-#define LONG_INT_MASK (BITS_PER_LONG - 1)
+#define LONG_INT_MASK (BITS_PER_LONG - 1UL)
typedef unsigned long ulong_t;
@@ -179,17 +181,46 @@
#include <asm/bitops.h>
+#if BITS_PER_LONG == 64
+
+#define OFF(addr) (((ulong_t)(addr) & (BYTES_PER_LONG - 1)) << 3)
+#define BASE(addr) ((ulong_t*) ((ulong_t)(addr) & ~(BYTES_PER_LONG - 1)))
+
+static inline void reiser4_set_bit(int nr, void * addr)
+{
+ ext2_set_bit(nr + OFF(addr), BASE(addr));
+}
+
+static inline void reiser4_clear_bit(int nr, void * addr)
+{
+ ext2_clear_bit(nr + OFF(addr), BASE(addr));
+}
+
+static inline int reiser4_test_bit(int nr, void * addr)
+{
+ return ext2_test_bit(nr + OFF(addr), BASE(addr));
+}
+static inline int reiser4_find_next_zero_bit(void * addr, int maxoffset, int
offset)
+{
+ int off = OFF(addr);
+
+ return ext2_find_next_zero_bit(BASE(addr), maxoffset + off, offset +
off) - off;
+}
+
+#else
+
#define reiser4_set_bit(nr, addr) ext2_set_bit(nr, addr)
#define reiser4_clear_bit(nr, addr) ext2_clear_bit(nr, addr)
#define reiser4_test_bit(nr, addr) ext2_test_bit(nr, addr)
#define reiser4_find_next_zero_bit(addr, maxoffset, offset) \
ext2_find_next_zero_bit(addr, maxoffset, offset)
+#endif
/* Search for a set bit in the bit array [EMAIL PROTECTED], @max_offset[,
offsets
* are counted from @addr, return the offset of the first bit if it is found,
* @maxoffset otherwise. */
-static bmap_off_t reiser4_find_next_set_bit(
+static bmap_off_t __reiser4_find_next_set_bit(
void *addr, bmap_off_t max_offset, bmap_off_t start_offset)
{
ulong_t *base = addr;
@@ -225,6 +256,21 @@
return max_offset;
}
+
+#if BITS_PER_LONG == 64
+
+static bmap_off_t reiser4_find_next_set_bit(
+ void *addr, bmap_off_t max_offset, bmap_off_t start_offset)
+{
+ bmap_off_t off = OFF(addr);
+
+ return __reiser4_find_next_set_bit(BASE(addr), max_offset + off,
start_offset + off) - off;
+}
+
+#else
+#define reiser4_find_next_set_bit(addr, max_offset, start_offset) \
+ __reiser4_find_next_set_bit(addr, max_offset, start_offset)
+#endif
/* search for the first set bit in single word. */
static int find_last_set_bit_in_word (ulong_t word, int start_bit)
